I've never had an animal which was already named, so I don't know if I would change the name or not, even if I didn't like it. I find that names tend to grow on you, so most likely I'd learn to love any name with time.
My friend's Rottweiler came with the name Sascha and neither of us particularly liked it and my friend did try to change it... but without much success. Sascha was and always will be a Sascha.

Taggart's name wasn't planned at all. For a couple of days I had tried calling him Kazuya (because I thought that was an awesome name at the time) but saying it out loud, it sounded too much like Sascha, so it was too impractical. Not to mention he just plain and simply isn't a Kazuya... that's a way too exotic name for a dork like him, lol.
I also called him Billy for a while. And Sofus. But then the TV series Taggart was on TV and I randomly decided to name him that and for some reason that was just spot on