is it perma linked to my email i registered with?
cause i wanna give my key to a friend but that email is my email for lots of other stuff

yes, by entering your cd-key into your battle.net account, its gonna stay there

is there a way to change it to another email address though?
or does my battlenet account stay the same and is unchangable

i think u can change it. go to battle.net and check account summary

You can change it. Make sure you know ur security pass.