I started a level 90 pally on PTR to try one out, and want to try out blacksmithing too. Problem is, when I switched from enchanting to smithing, it started out at 1, whereas the jeweling and enchanting at the start of the 90 came at 600. Is there a way to insta cap the proffesion on PTR?
No, it just copies the character from a template and all of them have JC and Enchanting so you can gem and enchant your own gear, there is no "insta cap"ing involved.
If you can get a character that's 60+ but below 90 you could probably have them boosted with the new store option but I don't know if that goes all the way to 600.