Changing 2nd Profession

Ok, I keep hearing talk about how you can change your 2nd profession once you hit 20. How so? Is this something you can access after you ascend? Seems like it would be a helpful way to unlock more skills for other classes without restarting your character all over again.

In the Crystal Desert there are NPCs who will give you quests that will allow you to change your secondary. I don't remember if you have to Ascend to access these quests or not. Once you have completed a quest for a class you can then switch to that class at will. The skills you had in your old secondary are not lost, but they will be completely inaccessible until you switch back to that secondary (and you will need to do the appropriate quest for that as well).

You do not magically gain any skills or skill points but you can access old quests that are appropriate to your new secondary to gain skills. For instance, I switched my Mesmer secondary to Monk, travelled back to Ascalon and was able to take the quests from the monk near there to get various monk spells. Then I switched to Necromancer, though I didn't bother to gain skills. Then back to Mesmer. Now that those subclasses are unlocked I can switch them around at will just by talking to one of the NPCs that gave me the quests.