Don't know about your query structure, but no you do not need to end with ;. Multiple queries per input box is also not supported, yet; more is to come for SQL Actions integration, but such talk is for a later time.
Changing a fields value will not function properly if the user is given a subscription from User Management, the reason being is you're saving the users profile data directly after changing a users subscription. Your query is fired and the value is changed, but then the profile is saved and the previous value will overwrite what your query changed. So testing with User Management will result in negative results always.