does this only work with rs3 bonds or osrs bonds too?
If you want to do it quickly you'll need bonds to allow you to change your name instantly.
If you don't mind waiting a bit you'll still be able to do it.
Account X = Username you wish to keep
Account Y = your main
Change username on account X once, then either use a bond to change it again (or wait a month) which will make the username available to anyone, at which point you instantly change the username on account y to the name you wish to keep.
Both, I'd assume.