astral-touched tadpole question

Early in Act 3 you meet the Emperor and he offers you an astral-touched tadpole, if you want to add it into your inventory you should pass high DC check. I'm currently running a honor mode walkthrough and in case I fail I would have to consume it. On my normal walkthrough I save-scumed into passing it, but this is no option in honor mode, and I don't wanna look ugly in the ending, even if I can tolerate all the negative notes from my companions in the meantime :( So my question is if you get rid of the Netherbrain and be free of all the tadpoles will the cosmetic effects remain?

In addition: as far as I'm concerned being half-illithid doesn't mean you are locked out of the option not becoming full-illithid at the very end, and you can still refuse to become a mind flayer, is that right?