Of course you can change the dog's name. I have changed lots of dogs' and cats' names. It happens all the time with strays and dumped animals. What do you call a dog when you do noy know it's name? You pick something, right?
If you know the dog's current name you can either mix the new name with the original name, gradually dropping the original name completely, or...like you would with a stray...just start calling the dog by whatever name you choose. It won't take long, if they are ever going to respond to the new name, for them to realize you mean them when you say the new name.
You can try several names out...to see which name the dog responds to best...or which one you like best for them...before settling on 'the' new name, too.
All of my babies...dogs and cats alike...have an 'official' name, and several other names/nicknames we call them. I changed one rescued black short haired mixed breed bitch from Spade to Samantha ("Sammy" for short...and because she preferred it) by combining Spade and Sammie and gradually dropping the Spade part. I also have one adopted long haired black cat that I renamed...but he didn't like the "Pepper" I chose and wouldn't respond to it. Finally, I asked him what he wanted to be called and started going through a list of names. Running out of ideas, I finally said to him, "I cannot think of anything else except, since you have some little wisps of smokey hair on your tummy..." and the instant I said "smokey" his head snapped around and he looked me square in the eye. He chose his name, Smokey, and he responds to it like a dog would...even will 'heel' which is really cute. He does reserve the right to act like a cat, too...sometimes. Although his name is Smokey he is more often called 'Mokey, 'Mokey-Mokes, 'Mokey Baby, etc.
Brody and Mia were named by their previous owners. The names were okay from my perspective, and the dogs were over a year old when I got them, and knew their names already...so, no reason to change. But, I would have changed their names in a heartbeat if I didn't like them or felt them to be inappropriate.
- Cat