I'm running N64 games via Mupen64 Plus (actually, it's wxMupen64 Plus-I couldn't run it from a CLUI, even if you switched me from americano to flavored decaf), and I have noticed that it's mentioned that it supports gameshark codes
and has some kind of cheat system built in, toggled by something in the Mupen64 plus config?, then you press the "G" key for Gameshark, and then....I dunno. I'm kinda stumped on how to use GS codes with this thing. Do you have to type them in manually and save them? I have also tried to load Hi def textures with no luck (it was for Sin and Punishment, a really good game if you like rail shooters-gets hard at spots, tho') without any success.