@dlowan,
Agreeing too with the determined sentiment. It also sounds like he's trying to come up with a self identity that he's happy carrying as a name.
Two quick stories.... My sister changed her name to "Nicky" when we moved to a new city. A few weeks after we moved the phone would ring and people would ask to speak to Nicky. None of us knew anyone named Nicky and said as much. It took a while but the upshot was that sis was trying to recreate herself in a new environment. We never called her Nicky but, eventuallyl, we did say, "Hold on, I'll get her" when she got calls.
Second story... a close friend of my daughter M all of a sudden announced that he was going by a different name. The family had recently gone through quite a bit of upheaval and everyone decided that if he wanted to be called by his chosen name rather then that was just fine. I guess he was trying to reinvent himself too.
I don't mean reinvent in any negative way, just set himself on an identity that he's chosen, rather than one that's been chosen for him. As to making a legal change???? I think I'd wait until he was older but 2.5 years says something.