Secondary class changeing

When are you able to change your secondary class?

after you ascend, there's a total of 5 secondary class quests to do, completing each one allows you to change to the corresponding class.

With that in mind...

What it also does is completely nullify what you've gained so far with your original secondary class in PvE (it doesn't affect anything in PvP... if its unlocked it remains that way).

It just means that you have to go collecting skills for the new secondary class you've chosen and completely say goodbye to everything you'd already accomplished with the first secondary class you had. It all depends on if you're willing to do that or if you want to eventually do that.

...keep that in mind.

Uhm. No.

You keep all your secondary skills on that character. You just can't use them until you switch your secondary back to the original class you had.