Changing Professions.

I know that you can change secondary professions via the Crystal Desert quests and at the Great Temple of Balthazar, but my question is when you do change your profession, say you don't like it, and go back to your original secondary profession, will you still have all the skills as before? Or would you have to unlock/buy them all again?
(Ex. W/Mo changes to W/R, then back to W/Mo would he still have all the skills he had originally)

Yep. You keep all your spells (and your pet if you are a W/R) when you switch back.

You don't lose skills when you change professions. So once unlocked, changing secondary profession has no penalty.

To add to the above - once you've gotten a particular secondary, you can simply change back to that secondary using the drop down list in the Skills & Attributes window (K). You could also save your W/R build as a template and any time you want to, you can simply load that template and your secondary will switch automatically.
For example, my Monk has, (among others), a RoJ build (Mo/Me), an HB build (Mo/E), and a BiP build (Mo/N) for VSF runs. I can switch to them at any time by simply loading the template.

Can I ask a question on professions too please!

I have a warrior made in Factions, and own all other campaigns, but I want my warrior to have a Dervish secondary profession. Do I have to go to the profession changer in Nightfall to do so, therefor playing through NF just to do it - OR - can I go to Senji's Corner in Factions and change it to Dervish there, because I own nightfall...or won't that work because he's the Factions profession guy?

Hope someone can reply back to me, thanks.

Pretty sure you have to go to NF.
Although there is also a Profession changer NPC in the PvP area, the great temple of bathazar that might work for you to get /D after you beat Naphui Quarter.

I *think* he will only change you to core or factions professions. It's been a long time since I bothered with Senji though

If that's the case, though, you have a third option. Go the Great Temple of Balthazar and talk to the profession changer there once you have beaten Nahpui Quarter. You will be able to change your profession for the same 500g to any from any of the campaigns you own

That's what I thought too until a friend went A/D at Senji's.

Yes at Senji's Corner you can switch to whatever profession is unlocked on your account for 500 gold each..