Originally Posted by
Aldun
Certain professions (Bs, Alch, Tailoring etc) have a Specalization after you reach a certain level (Armor/weaponsmith, mooncloth tailoring, potion master etc). By doing the questline for one of these specalizations, you will learn aside from the normal skill also the Spec skill (which opens the same window).
If you now unlearn the profession from the Skills tab, the Specalization will stay and you're able to learn a 3rd/4th/5th etc professions!
I tested this on several realms/cores and didn't find a single one where it didn't work.