So I recently returned from a very long absence in game. I started a new server and got Gold premium to assist leveling, not realizing they had implemented the new EXP and DC premiums.

Is it possible to buy one of these (I need EXP) and have it overwrite or replace my current Premium service? If not, what would happen? Would it just tack on to the end date of the premium I currently have? Would it disappear? Thanks in advance whomever can clarify this for me.