Sadly i doubt admins could do much about impersonation, it could be a funny coincidence that he had that identity before you (which is never the case but still)
If your friends are loyal a good thing to do is set up a little password with them and whenever the impersonator decides to trick your friends the friend can ask for the password
I do things with stuff.
There's always someone who wants to be you so bad so don't worry about it.
Just don't give them your GraalID because that's when they can find your customs.
If you're been harass by someone that looks like you then harass them back by putting their name and their custom or you could just follow the person 24/7 and Pk and just talk to him/her until she agrees to redound the custom. That's what I did and it worked lol