Key_pressed with the -1 ability and also key_pressed to key_lastpressed and key_any(x) == X and also the key_hit.

But if you have the pre-mapped key in a array if(i[0]) jump and if(i[1]) walk
then you can remap by recording on the menu page the replacement string i[0]=key_for_str() then forever cycle your array in each frame. But remember to reset key_pressed with the -1 where needed or compare to key_last where needed. And key any() actually helps at times.