I would imagine it should be fine, my brother changed his name when he was in year 6 I think from memory. He was previously known as Ed or Edward and decided that he wanted to be an Eddie. The school and his friends took to it without a problem but I took about a year to come around. I had so much trouble remembering the change after always referring to him as something else. I also kept thinking he would regret it as he was choosing a more 'child like' name over a more adult one, just as he was about to enter a older phase of his life. He is now 30 and still known as Eddie!

Personally, I love the idea of children having the ability to choose their own name variation. I like the sound of your son taking ownership of his identity and being proud of it, just gorgeous.