You could just swap names and colours.. not the defines? This wouldn't swap elements, meaning saves will stay healthy. But if they are under protection then it's fine by me.
You know what? Scratch the making uranium fissile bit. Maybe just switch the name, i.e. URAN is now PLUT and PLUT is now URAN. It won't affect the actual elements themselves.
It sounds to me like TPT is about to need a better engine. Why not start with that before we do anything else with elements or making any other additions to TPT? That way, we could add a lot better things later without making it run slower.
It'll need a ... 1) build_save function 2) create_particle function 3) load_save function 4) browse_saves function 5) console function 6) create_brush function 7) modify_brush function 8) select_element 9) newtonian_gravity 10) photoelectric 11) cherenkov 12) save_stamp 13) create_wall 14) load_stamp 15)browse_stamp 16) delete_stamp 17) delete_save 18) browse_own_saves 19) favorites 20) tag_add 21)tag_remove 22) vote (What if we'd renew it as one to five stars?) 23) and so on