Lewdly change of main spicies

[SouliK]

There is some way to change a empire main race after it's been take over or reemplaced?

[Jurassic Parka]

Not sure if you still need help with this, but this is somewhat possible in the base game if you go the genetic ascension route. You can't just change it to whatever species you want, but you can change the portraits to something from the same group ( ie. humanoids, reptiles, arthropods, etc. ). 

 

An example would be if you are trying to modify an Avian species, you can't give them a Reptile portrait, but you can change them to any other Avian portrait.

 

Might be a mod on the steam workshop that further expands on this feature though.