I'll probably make it so the encounter gameshark code won't do you any good. I don't want it to be possible to cheat to get the pokemon you like. Well, that wouldn't be much of a problem since most people like playing the game fairly either way (and doing stuff like encountering a Porygon shouldn't be bad at all), but the thing is, there will be replacements that may not be obtained at all and they could still be encountered with the same gameshark code.
I just checked it and it's going to take only a little while to disable the encounter gameshark code from running the way it is, so I'll just do that. Sorry for all who like using that fairly.
But anyway, Porygon should evolve by level. It might not though since I haven't intended it to be obtainable (and thus, may not have changed its evolution method at all).