Just be aware that, although they will look like the other Koopalings, they will still have to sprite-swap (and, therefore, act exactly the same as) one of SMBX's pre-programmed boss NPCs (unless you know how to use LunaLua).
While it is possible to make
fully custom bosses in SMBX, it takes a lot of time and dedication, so most people stick to using the pre-programmed boss AIs. However, you should also avoid just using the pre-programmed bosses by themselves in empty rooms all the time, as that would get boring for the player. For more info, check out my tutorial on the subject:
http://www.smbxgame.com/forums/v ... =81&t=8890