As far as I know, changing your name in any way erases everything and there's no way around it. Even changing an uppercase letter to a lowercase letter is enough to have everything deleted. I think that's kind of silly but it's how it is.
You can keep track of you stats quite easily with Spatula's stat program (PM him for the download if you want it) by loading all the tours you flew with your previous name and then adding your new name to it, but perk points and achievements as well I think are gone forever.