It mention in the update notes that for RP chars, you can only switch to the professions you've already unlocked. Ascension/Weh No Su/Nightfall's equivalent are required for this, so yes, in turn, you need them to change professions.
Well you need to do the profession quests first, and they require ascension. So yes.
Or you might be able to quick-switch after buying them in Senji's Corner.
