By changing your citizenship, you can also change your class. Be aware, on completion, your spells and abilities will be reduced to (Apprentice I) level. If you wish to stay aligned to the same faction, you must become Exiled and complete the quests to re-align with them.
You may only change within your own sub-class (I.E. a Warlock can become a Wizard, a Warden can become a Fury, etc.)