which emerald codes won't corrupt my save?

keep an in-game save from before you turned any code on, not just a save state. if a code has already written junk into the save file, loading a state from after that won't help you.

it's less about which code and more about how you use them. the ones that bite people are walk through walls, pokemon modifiers that write to the party slot, and anything that sets story flags. item codes and wild encounter modifiers are usually harmless. what keeps a save safe: - back up the save file before you try anything new - one code at a time, not a pile of them - turn the code off before you save in game - never save while standing somewhere walk through walls put you if a code makes the game act strange even once, load the backup rather than pushing on.