secondary profession from another campaign?

I'm playing PvE with the GW trilogy. How do I change my secondary profession to one from a different campaign? For example, I started in Prophecies, but I want my secondary to be a Paragon from Nightfall. Thanks.

To get paragon or Dervish secondary, once you've ascended in Prophecies, you'll have to go to Nightfall and play through the storyline until you get to the Command Post.

There is also a Profession Changer in the Great Temple of Balthazar who can change your secondary to any class available to your account.
http://www.guildwiki.org/Profession_Changer_%28NPC%29

and its faster to ascend in factions than prophecies (just have to do the nahpui quarter mission).

It is faster to ascend in the other campaigns, but if your first Ascension-equivalent mission (Augury Rock for Prophecies, Nahpui Quarter for Factions, and the "Hunted!" quest for Nightfall) is Augury Rock then you get a bonus 50,000 experience which you won't get for completing Nahpui Quarter or "Hunted!" first.

True, but what use will xp be? it's only another skillpoint. If you haven't lvl'ed up to 20 yet when you get to either of the ascending points you did something wrong.

It's not doing something wrong if you intentionally skipped a lot of the missions to get to ascension. I once fought and killed the doppleganger on a level 13 necro. The extra XP took me immediately to lvl 18, (close to lvl 19) which was a real time saver.