Renaming is fine, I always like to give my animals a "fresh start'. I especially like to find names that have a good meaning for them. My most recent horse had the name Mariah, which means "bitter". I couldn't stand the thought of that, so I looked for a new name, & chose Merci, which means "compassion". We had a great partnership!
With a dog, they will get used to the new name fairly quickly, more so if you use it often. A trainer gave me a tip that I found works quite well:
If you use the new name in conjunction with a command, the dog will learn to associate the new name the way they did the previous one. For example, if you are renaming Pooch to Fido, you would say "Fido, sit" he will hear the "Fido", understand the "sit" give the behavior & get rewarded for it. Then you can use "Fido, heel" "Fido, fetch" "Fido, come", you get the picture.
Of the dogs I have in my house, I will say, not one of them has only one name. Most of my dogs have at least 2 nicknames, in addition to their normal name. It doesn't take more than a day or two of them hearing a nickname to start responding to it the same as their name. They love us, & just want to hear us calling them, whatever that may be. =-)
Good luck with your new pooch! T.