Everything is possible by writing the source code. However, I don't think that would be a good idea add new transformations to a game like an MMORPG that should have some balancement between the various races and classes.
In the humans/saiyans case is pretty simple: Oozaru, SSJ1/2/3/Red/Blue. But what about the other races? Majin absorbtion and Namekian assimilation are not real self-transformations. Ideally speaking those would involve a second "person", like a fusion. That's why I don't think it is a good idea.