i''ll try to explain this best i can without too much rambling.
my son has a double barreled surname, his dads name hyphenated with my name. At school he just uses my name as he prefers to drop his dad's name cos of everything that happened. everything else is his legal name, bank account ect.. which i have no problem with at all. But now that his step dad and i are getting married in June and my son knows i will be changing my name he now wants to switch his name so it will his stepdad's name hyphenated with mine. Legally I can't do this as his dad would never agree so I plan to keep his legal name til he is old enough to change it himself if he still wishes. But for example at school could he be known by his new chosen name.