Report Builder - using id that is not User!UserID for row level security

I am trying to learn about adding row level security to a reoprt, and I have been able to do it like in the docs. The issue that arose is that I was told that the User!UserId that is being used will not be used in the future. So I was trying to find a way to be able to do row level security by trying to get a different id.

1. Is this possible? or is User!UserId the only option?

2. Does that mean I need to figure out a way to change the current User!UserId name to some other id. 

Thanks for any help