Hi Frank,
This can be done. I checked and unfortunatly cannot Find the area where to do it. Anyway, I too had my UserName changed in 2013 I think Peter van Es did it for me. You will still need to use your original UserName to log in, however, the one you like to change it to will appear in the forum. So just wait Peter will properly see this post and do it for you.
Best,
Dieter