roxy! i’ll make a post because the message system don’t work!
example: your original blog name was - ORIGINAL. and your new blog name is: NEW.
go to the blog titled ORIGINAL (the place where you saved your url)
go to settings > url > check custom domain name > fill out as directed

this way, every time someone clicks on a like directed to your old blog name - it’ll redirect to your new one! even permalinks.