Bahamut Replace Doom Gaze/DeathGaze?

Hello again Sirs/Madams I have asking about fought Doom Gaze Is it Ok to replacing Doom Gaze to Bahamut itself to fought FF6 characters?I really don't know how to replace the sprite of Bahamut(FF5) from Doom Gaze and what new dialogs for him and towns people that talking about Doom Gaze in W.O.R.! If you asking me why should I replace Doom Gaze for Bahamut?I play the GBA version of FF5 Bartz team(FF5) they fought Bahamut in the Mountain(I don't know what is the name) and defeat him to turn into summoner.So I have to do this to change different so the FF6 characters fought Bahamut itself instead Doom Gaze but like I said I don't know how to replace it and new dialogs....I know this is not big deal of yours but I have to learn and figure out.