Actually made a mod--had a lot of help!
This mod will change Carth's appearance in various scenes in SW KotOR II: The Sith Lords. In most scenes, Admiral Onasi will have some gray hair; he's aged a little bit. When appropriate, this mod will keep Carth from looking older than he did in KotOR.
This mod is compatible with cjt0202's Admiral's Uniform for Admiral Onasi 2.1 (Carth's Eye-Searing Armor Fix), however, one file in my mod will overwrite one of hers (specifically, p_carth001.utc). However, it doesn't matter because they are identical. If you have an earlier version of cjt0202's mod, you'll have to copy my p_carth001.utc into Override; they're still compatible.
Kha has graciously provided remapped head models for Admiral Onasi which helped free up the reskinning.
There are also three versions of Carth's texture, and an HTML fle is included so people can see them and decide if they want to use one that's different than the default.