L.M.
Here is my opinion...you picked the name, you named him, that is his name....use Dimitri if you have another. Or keep his name and call him Dimitri as a nickname...I know that sounds weird but it is no weirder then renaming him at 18 months.
My sister wanted to name her son Justin Kyle and call him Kyle. He hubby wanted a junior so he is Richard Allen XXXXXX Jr. and we call him Kyle. It was the compromise that they reached.
I wanted to name my daughter Cheyenne Nicole but her dad wanted something different. Came up with every other name possible and the only one I liked was Madison but I loved Cheyenne Nicole. I made a compromise, he name is Madison Cheyenne but she is know as Cheyenne (her nickname is Shiny Girl thanks to a little girl at daycare that could say Cheyenne).