Is it possible to make Enemies and NPC's become player characters? [FE5]

[Jedi]

I know the knowledge of how to hack fe5 is extremely extremely limited but I wanted to ask you experts if any of you knew if you could make the likes of say.. Altenna from her brief cameo in Chapter 23 into a player character to use and such [i had an idea with her so that's why I'm asking]

Also know i'm a bit of a novice in terms of fe hacking in general so if you could explain in the most simple terms possible or if its even possible in Nightmare. Thanks in advance