What do you mean by "assign growth potentials"? If you want a projection of how a player can develop (which clearly is a scouting feature), you can use Genie Scout that has this option already.
Changing a regen's portrait seems like a pretty vague thing to accomplish. Even if it was possible, you'd need certain presets and whatnot... which would make this a pain to put together. And I'm not so sure a lot of people would want such feature. I know they want better hairstyles, but that's about it.