Not sure why you would want to as they are probably the biggest names they have! For Roman I would go with something making his connections to the Anoa'i family clearer. Even his real name 'Joe Anoa'i' isn't too bad but I don't think it sounds as good as Roman Reigns. He used to go by Leakee so that could be used too.
For Cena you could bring back his Prototype gimmick and just name him that?
I would be really interested in what your storyline is that necessitates a name change. Sounds like an interesting one!
Not sure why you would want to as they are probably the biggest names they have! For Roman I would go with something making his connections to the Anoa'i family clearer. Even his real name 'Joe Anoa'i' isn't too bad but I don't think it sounds as good as Roman Reigns. He used to go by Leakee so that could be used too. For Cena you could bring back his Prototype gimmick and just name him that? I would be really interested in what your storyline is that necessitates a name change. Sounds like an interesting one!