Ah, the joys of finding the elven court bow that make you realize, wow, its really worthwhile for my sorcerer to get the martial weapon feat. However, when you realize you had picked a light armor proficiency feat, and then further realize that it will never do you any good since you intend to only use the battle robes in the game, you have a problem.

Not only have I made the mistake of choosing a half-elf race for my sorcerer (which isn't too bad, he is still cool) but now I screwed myself outta a feat as well.

Is there any editor or cheat out there that will allow me to change my feat from light armor to a better feat? I hate the fact that I made a permanent mistake like that.

You can always use the debug mode to add and remove feats, but that will tag your character as Illegal.