Changing a name shouldn't cause big problems. What you want to do is build a positive association with the new name. I clicker train name response with my dogs and use the same method with the dogs at the shelter that I work with. I say their name and at first any response even an ear twitch, I click and treat. After a couple click/treats they usually start turning their head at the name if they weren't already so I start clicking the head turn. Pretty soon, when they hear their name they are turning toward you then moving toward you as they are rewarded more and more for responding to the name.
When I was with BEAR-Basenji Education and Rescue in OH, we changed a name from Christopher to Trooper. I think he was around 5 years old. The previous owner did call him Christopher and it was even painted on his crate! He learned his new name within a week and I was surprised. it only took him that long. Perhaps he did not like his previous name!
Dogs learn quickly, especially if their former home was not so nice. Then a new name is perfect. We changed Nicky's name from Nyako, picked a "sound alike" and she learned it pretty quickly, well, as much as some basenjis ever "learn" their name. Some days she doesn't recognize it at all, haha.
Eddie was Skippy, I looked at him and called him Fast Eddie and it stuck. That boy knows his name all the time!
And do tell, what is the awful name???