Ace Custom

An ace custom is a piece of technology -- a Humongous Mecha, Space Fighter, a particular weapon, or something similar -- that differs from the normal model due to being tweaked in order to better fit its user. Said users are typically Ace Pilots, and their equipment is customized to their specifications -- thus, ace custom. The extensiveness of this customization varies widely, from simply giving it a new paint job to actually having a completely unique machine built from scratch. Closely related to the Super Prototype, an ace custom will usually be significantly more powerful than a standard model.

Normally, ace customs reflect their user's combat style -- a pilot preferring high-speed combat will boost their engine output, a gunslinger with Improbable Aiming Skills will add scopes and bipods for increased accuracy, etc. This may allow them to be Weak but Skilled, if their equipment doesn't has as much raw power as their opponent's, but it's so tuned to their strengths that they can compete anyway.

Anime and Manga

 * Used frequently in the Gundam metaseries, from Char's iconic red Zaku II in Mobile Suit Gundam to Amuro's custom-build-from-scratch Nu Gundam in Chars Counterattack.
 * Super Dimension Fortress Macross has Maximilian Jenius and his wife, Zentradi defector, Milia Fallyna, being granted the privilege to give their mechas distinctive paint jobs for being the top pilots of the force.
 * There are two ace custom Valkyries, Hikaru's that has a triangular visor, two guns and a "chin" (VF-1J), and the Skull-1, with FOUR guns on the head (VF-1S). Both have custom paint jobs as well - Hikaru's is painted in red stripes, the Skull-1 is painted with black and yellow ones, with prominent skull-and-crossbones.
 * Based off of side info like model kit manuals, Brera's VF-27β is indeed an Ace Custom, while the VF-27γ is the "common soldier" version.
 * Tengen Toppa Gurren Lagann has a number of unique mecha, but of particular not are the Four Generals, each of which has a custom mech despite their minions using basic Mecha Mook Grappals.
 * Code Geass features several ace customs. The Knights of the Round are an elite, 12-person ace custom squad piloting highly personal, one-of-a-kind mechs, including the Transforming Mecha Tristan. The Japanese side has Shinkiro and the Zangetsu as their ace customs.
 * Admirals on both sides in Legend of the Galactic Heroes get ace custom flagships, which tend to be slightly more powerful than their factions' regular fleet ships and serve as Ships of the Line in their Standard Sci Fi Fleets.

Literature

 * Mack Maloney's Wingman series features numerous ace customs -- the series is set in a post-WW 3 Divided States of America, so the combat aircraft flown by many of the protagonists (including the main character, Hawk Hunter) are practically their personal property.

Live-Action TV

 * A two-episode story on Space: Above and Beyond featured "Chiggy Von Richthofen", a enemy Ace capable of wiping entire squadrons of Earth fighters by itself. "Chiggy" flew a special version of the standard Chig fighter that had some kind of stealth technology making it invisible to Earth detection and targeting systems, was invulnerable to cannon fire, and in general displayed greater speed and maneuverability than any other fighter in the show. Also, its nose was painted with a human skull and the phrase "Abandon All Hope".

Tabletop Games

 * Done in the BattleTech animated series, and in the world setting for the original game as well. Many "ace" Mechwarriors have unique mech variants, such as Justin Allard/Kai Allard-Liao's Yen-Lo-Wang Centurion or Natasha Kerensky's "Widowmaker" Daishi.
 * OmniMechs, with swappable hardpoints, were pretty much specifically invented to allow players to build their own ace customs.
 * Warhammer 40000's own Maximillion Weissman had his own custom version of a Baneblade built. Functionally however it was near-identical to a normal baneblade, except for Weissman's superior crew which gave it slightly superior stats. Commissar Yarrick also has his own version of the Baneblade, the Fortress of Arrogance, which does have more noticable modification. It was presented to him as a gift from the Adeptus Mechanicus.
 * Tau Commander Farsight has his own Battlesuit customized with the unique Dawnblade he found, subsequently making him the only tau unit dangerously competent in close combat, which suited his bloodthirsty tendencies.

Video Games

 * The Original Generation mecha of Super Robot Wars is overloaded with Super Prototypes and Ace Customs, there's far too many to mention.
 * Ace Combat occasionally has custom paint jobs used by enemy Ace Pilots. Frequently, you can use their paint job if you defeat them.
 * Valkyria Chronicles II: throughout series there are weapons that the Aces use; defeating them either earn you the blueprints for said weapons, or the weapons themselves.
 * Getting technical, any of the titular mecha from Armored Core are ace customs. Each one is a specially built engine of destruction that accommodates the pilot's fighting style and can wield an astounding array of weaponry. Also, when Armored Core 4 appeared, mass production models of Cores appeared as Mooks-- Normals. The newer NEXTS now being the weapon of choice for Ravens, err Lynx.
 * Xenogears tends to go the ace custom route to an extreme. Named characters' Gears tend to be unique models custom-built for the pilot (or else Lost Technology Magitek that can't be reproduced at all), while mass-produced Gears are used by Mooks.
 * Custom Robo is, as the name suggests, all about ace customs.
 * Sword of the Stars features an ace custom flagship, a jacked-up CnC mission fused with a barrage mission. It costs a fortune, and you can only have one at a time. Oh, and losing one hits your morale harder than having something death star a major colony.
 * The main characters of Danball Senki all use special LBX, either customized by themselves or done for them by prominent LBX producers (justified as good players are hired to test new products).

Western Animation

 * The e-frames given to Able Squad in Exo Squad were all modified versions of the usual models, testing new features which inevitably turn the tide in the first battle they are used in.
 * Phaeton's personal Command E-Frame is capable of shrugging off direct hits that would destroy a normal E-Frame. He later has it further customized with medical equipment to help treat his automutation syndrome.