Below are the various methods of leaving or joining the City of Neriak as of GU56. 
Citizenship quests can be done without betraying if you are either leaving Neriak to head to another evil aligned city or coming from an evil city to Neriak. Citizens of Neriak can betray to change to a city of good alignment while good citizens can betray their cities and choose Neriak as a destination.
To begin the process of betraying Neriak, you must first save a child called Matteus Gaines( 80,23,164 ) , who is being beaten up by thugs in the city. He will direct you to speak to Ambassador V'Nox( -496,23,206 ) , who will warn you of the consequences of betrayal and finally send you on to Magister De'Pater( -276,29,204 ) .