I have a "friend" (we will call him ME) who wants to make some NES games for friends that feature their likeness instead of the hero of the game. The usual, standard fair of games like Mario, Boy and his Blob, Contra, ect.

I searched around a bit and couldn't find much on the subject. Do I need anything special to get into the rom, change the sprites and save the rom as playable with new sprites?

would make great Christmas gifts.

This would be better suited in the Brewery section. I'm sure someone there could help you out.