Changing primary character's secondary

[Ithim Sigilscrye]

Anyone far enough into Nightfall yet to tell me when I'm given the option to change secondary class on my character? I know the Hero Henchies can change whenever, but the main character doesn't have that capablility until I learn another secondary other then the one I initially chose.

[Shardie]

Sunspear Sanctuary. You unlock this ability by doing the "Command Post" quests

[Death Dealer Damon]

Sunspear Sanctuary. You unlock this ability by doing the "Command Post" quests

How far into NF is that?