Changing secondary professions

I currently have a lvl 20 ascended W/Mo character. I am aware that once a character has ascended the secondary profession can be changed by completing the appropriate quest among these:

The Elementalist's Path
The Mesmer's Path
The Monk's Path
The Necromancer's Path
The Ranger's Path
The Warrior's Path

(Retrieved from "http://gw.gamewikis.org/wiki/Secondary_profession")

So for example I complete 'The Elementalist's Path' and change my profession to W/E. Then I complete 'The Monk's Path' and change back to W/Mo. Will I have to complete these two quests over and over again to keep switching my professions? Or is it enough to do these quests just once?

No. All you will have to do, is if you've already completed that quest, you just have to talk to the person with that quest and you can change your profession back.

no and you don't have to do a quest to change back to your original secondary either. Once you change professions then you can go to any of the profession quest ghosties and they can change you into the secondary of your choice provided you have done the quest for that profession.

its enough to do the quests just once^^