Heya dude =)
I've got a ybr 125, there are a fair few of us on here... Mostly with tyre issues thou lol!
As for de-restricting... all i've heard is that the ybr is just restricted by a small engine. (bit like honda cg's) so i dunno if ur gonna be able to find much info...
however! If you do i'd love to know it too as i've recently passed my test on my ybr and wud consider derestricting mine too =D