Can you use the name Gwen as a double barrelled first name?

I think Gwen by itself is better than as a double-barreled first name. I love Gwendolen (I prefer this spelling to the 'yn' ending). By the way, it's Gwyneth, not Gwenyth, so it might not lend itself to Gwen as well. I would just go with Gwen if that's what you like!