Since all my birds have been rehomes, I've kept all their names as they came to me. Most of them new their names and since none of them were truly offensive, I chose to keep them...Even though I might not necessarily like the name, or I don't feel the name fits the birds personality, that's what its been called.
I feel that even though they might come from a not so nice back ground the move is stressfull enough in itself let alone trying to call the bird by another name would only be more confusing and stressfull for it.
I guess that if one came to me with a truly offensive name, I would try to find something that rhymed with the name or was very close in sounding the same. Such as the example of coming with the "n" word I'd probably have changed it to tigger or digger etc..
In my Blue and golds case She came with the name Bailey...she was 18 and had been owned by the same person all those years so changing her name was out of the question as far as I was concerned...however, I have added on to her name and call her Bailey Boo or Bailey Boo Boo and she seems to enjoy it because it started out because we were playing peek a boo.
My Cockatoo, Cowboy was basically the same story, 15 years old one previous owner and they named her before they had her DNA'd Well actually they didn't have her sexed, I did...and she's a Cowgirl...but the she knew her name and says it all the time so...Cowboy she is.
Andie has a B & G who came with the name Maegan, the bird was only 4 I think hadn't been sexed and so After Andie DNA'd Meagan, she changed his name to Magnum it sounded very close to how he said Maegan and now he says Magnum
So there's my nickels worth...