Orphaned/Sandbox/Altered Uniform

When a character makes changes to their uniform in order to stand out, they're wearing an Altered Uniform. There are a number of reasons why they might do this. They're often a Rebellious Spirit doing it specifically to defy authority (Japanese Delinquents in particular take this to an art form, considering that school uniforms are much more common in Japan than in the West) or a Blithe Spirit just trying to spice up those boring old uniforms. The meta-reason for this is usually to give characters Distinctive Appearances that makes it easy to pick them out of a crowd, so you can tell at a glance who's a main character and who's just a Living Prop.

Unlike Uniform Refusal, an altered uniform will still be recognizable as a uniform, it'll just be distinct somehow. Maybe they ripped off the sleeves or added a Useless Accessory or two. Maybe the cut of the uniform is the same, but it's a different color. Whatever changes they make, though, it will reflect their personality.

If they change they make is obviously unintended, but still within the letter of the dress code, then they're Technically In Uniform. If the change they make is intended to show off their sex appeal, then that's an Altered Uniform Of Sexy. See also Unique Uniform (when they have permission for their distinct appearance) and Personalized Uniform (when everyone's uniform has individual touches).

Anime

 * Shugo Chara: Amu has one with a slghtly higher skirt, a loosened tie and a black jacket and shirt combination, complete with "x" hair -- clips, of course, rather than the usual Seiyo girl's uniform.
 * Hokuto from Cromartie High School wears a white uniform instead of the ordinary black one, due to his over which school he transferred to. He presumably keeps it just to stand out.
 * Team Rocket's Terrible Trio in Pokémon don't use the standard black uniform that normal mooks use; they made their own white uniform to stand out.
 * Mendou in Urusei Yatsura wears a different uniform just to show off how rich he is. Ryuunousuke wears the standard boy's outfit... at her father's insistence (the latter being in denial about not having a proper son).
 * Sailors Uranus and Neptune are the only senshi in Sailor Moon to wear short gloves rather than elbow-length ones. Given their Aloof Ally status, this sets them further apart from the others.
 * In Magical Girl Lyrical Nanoha, the Barrier Jackets of most named characters are unique and very different from those worn by the generic Space-Time Administration Bureau combat mage. However, they do wear the standard military uniform of their branch when not in battle.
 * Several characters in Mai-HiME have customized uniforms, mostly the head members of the student council, who wear different colored uniforms, including Shizuru (khaki) Haruka (green) and Reito (black). Natsuki also wears a hooded white sweatshirt with her uniform instead of the usual blouse, and Haruka's blouse is short-sleeved when she wears it with a vest. In Mai-Otome, Arika's uniform has pink trim, unlike the green in most Coral uniforms. The top Pearl wears a white uniform instead of gray, with red trim instead of yellow. Mai, however, wears bright orange trim with her Coral and Pearl uniforms.
 * Alice L. Malvin from Pumpkin Scissors wears a yellow uniform while everyone else in the army wears an olive one.
 * Jo Jos Bizarre Adventure: In the third arc, Jotaro wears a heavily modified version of his school's male uniform. He even hires a tailor to make an exact copy of it when the original is destroyed in a fight.
 * In Neon Genesis Evangelion, Toji Suzuhara is always wearing a track suit jacket over his school uniform. A few NERV personnel make alterations, too: Misato with her red jacket, Ritsuko with her labcoat, Kaji and Fuyutsuki wear darker-brown versions, and Gendo has a black jacket.
 * In Hidan no Aria, Riko modified her school uniform to be more Lolita-like.
 * Itsuki from Heartcatch Pretty Cure wears a white version of the male uniform, not just to show her status as granddaughter of the principal and Student Council President, but also to emphasize her Bifauxnen nature.
 * Yusuke Urameshi from Yu Yu Hakusho wears a green school uniform instead of the standard blue. His reputation as a violent delinquent keeps the staff from trying too hard to enforce the dress code on him.

Comic Books

 * The Mildly Military Swedish comic strip 91:an (Which could be described as a Swedish version of Beetle Bailey) have the namesake main character private 91 Karlsson still wearing the same old blue uniform he wore when the comic strip started back in 1932. The rest of the characters however, wear grey uniforms from the 1960s.

Film

 * Some of the Star Trek films see our heroes wearing alternative uniforms, that have clearly been designed for Starfleet use, but are typically more casual in look than the standard uniform. In particular, we have Scotty's black "engineers jacket", and the Power Trio all get alternative uniforms in the fifth film as well.
 * Pretty much all of the Colonial Marines in Aliens have this; the only exception is Lieutenant Gorman, who wears a pristine, fresh-out-of-stores uniform, presumably to emphasize the fact that he's completely inexperienced.

Literature

 * Corran Horn in the X Wing Series keeps his flight suit and X-wing colors from his days in Corellian Security -- mostly because his X-wing was his personal property, rather than assigned to him by the New Republic.
 * In A Hero of Our Time, Cadet Grushnitsky chooses to wear a Private's coat over his uniform, much to the chagrin of his peers.

Live-Action TV

 * Star Trek seems rather permissive about allowing nonstandard additions to the standard uniform for cultural reasons. In The Next Generation, Worf wears a Klingon sash/baldric and Ensign Ro has a Bajoran earring; in Deep Space 9, Major Kira's uniform has certain feminine accents uncommon to the standard design, and Odo's was modified from the standard Bajoran security uniform.
 * Every Sixth Ranger in Super Sentai and Power Rangers has a different style of uniform than the main team. Sometimes it's just a color reversal or adding a chest piece, sometimes it's a full suit of armor or actually being a Humongous Mecha or Metal Heroes. This applies even to their unmorphed outfit -- the rest of the team will follow a pattern, but the Sixth Ranger will be different.
 * On The Fresh Prince of Bel-Air, Will turns his blue school blazer inside out so that that the patterned red silk lining is on the outside, and accessorizes with a backwards baseball cap. In some episodes, he also wears his tie Necktie Headband style.
 * Lieutenant Jim Dangle from Reno 911 wears shorts with his uniform, which he states he had to specifically ask the state for permission to do.

Video Games

 * Popular in various Final Fantasy entries:
 * In Final Fantasy VII, First Class SOLDIERs are allowed to use personal equipment, including changes to their uniforms. In addition, the Turks wear matched suits, but Reno wears his with no tie and with his shirt untucked because he's just that Badass (or lazy, whichever).
 * In Final Fantasy VIII, the one time Seifer wears the SeeD uniform at all, he leaves his the jacket open and wears a vest underneath it.
 * In Valkyria Chronicles, many of the members of Squad 7 had some variation on their uniform. This would be avoided by Welkin, who wore his commander's uniform exactly as it was meant to be worn, except he is the only person who doesn't have a uniform variation and therefore stands out because of it.
 * In Tokimeki Memorial 1 and 2, Rei and Mei Ijuin, as heirs of the filthy rich Ijuin Family, are allowed to wear variants of their respective schools' regular uniform. Becomes a plot point in Tokimeki Memorial 2, as if Mei is in Tokimeki Status with the main protagonist, . Small variations to the standard uniform -- usually a different shirt and/or tie -- are also common throughout the Girl's Side games, especially on the parts of the more artistic and/or fashionable characters.
 * The Persona series uses this extensively:
 * In Persona, each of the playable characters have their own personal flair. The protagonist, Maki, Eriko, and Nanjo add an earring, compact-amulet, orange scarf, and a light blue #1 scarf respectively. Yukino wears a much longer skirt than normal, Masao/Mark wears a turtleneck, a Nice Hat, an earring, and carries around a yellow tagger's backpack. Hidehiko wears a purple long-sleeve shirt with his jacket half open, numerous bangles, red boots, and has a pair of sunglasses perched on his head. Yuko wears a skirt that is half the length of the standard skirt and she wears a blue-with-green-stripes jacket and baggy knee-socks. Reiji goes around with his jacket open and no shirt on and wears a pair of American flag motif Fingerless Gloves.
 * The Persona 2 duology has Eikichi "Michel" Mishina, who wears what appears to be a kilt under his jacket over his uniform pants.
 * The only ones that actually wear proper uniforms in Persona 3 (including the PSP version) are the female protagonist and Robot Girl Aigis, and even then, Aigis wears the winter uniform even in summer in order to hide her robot joints. The male protagonist wears his winter uniform blazer unbuttoned and a pair of engineer-style boots. Junpei always wears a ball cap and a blue shirt instead of a white one. Yukari wears a choker, a pink sweater instead of the winter uniform jacket and a shorter skirt. Fuuka wears a green turtleneck instead of the white shirt. Akihiko wears a red sweater vest and neither he nor Mitsuru ever wears the uniform jacket. Mitsuru at least has the excuse of "her father pays for this school", but the others don't. Ryoji also wears suspenders instead of a belt, rolls up his sleeves, and wears an absurdly long scarf instead of the uniform jacket.
 * Persona 4 is similar to its predecessor in that only The Protagonist wears the correct uniform, but the winter version jacket is unbuttoned and he has his shirt untucked with both versions. Chie wears a green sports jacket over her winter uniform and wears the summer uniform correctly, with her jacket tied around her waist; she also wears bike shorts under her skirt for both uniforms. Yosuke is always wearing headphones around his neck and foregoes the winter uniform shirt for a longsleeved V-neck shirt, but wears the summer uniform shirt with a shortsleeved V-neck shirt under it. Yukiko wears a red sweater or cardigan over her uniform top, depending on the uniform version she's wearing. Kanji wears his winter uniform jacket like a cape and only wears the uniform pants during the summer. Rise wears the uniform correctly in the summer, but the only variation she makes to the winter uniform is that she wears a white turtleneck under the uniform top. Naoto does wear unaltered winter and summer uniforms...but it's the boy's uniform, which she continues to wear even after her real gender is revealed. The only time she wears a girl's uniform is if she's your Christmas Date and you request her embrace her femininity.

Web Comics

 * El Goonish Shive has Tedd and Susan play mix-and-match with their male and female school uniforms to protest Moperville North's strict, sexist (and short-lived, at least in-universe) school uniform policy.