You deffinetly don't wanna drop the low-end skills based on level but probably do wanna drop high-end skills if the user is to low to have them.
/GameData.Self.TradeskillLevel
/GameData.Self.TradeskillSubClass
Will give you the stuff needed for IFs.
Level tests should be a simple button.visibile=(TSLevel-1)>SkillLevel.
You could minimize the class-based IFs by nesting each set of tier 2-5 class skills in subpages and do 1 IF for the whole lot, since out-of-class doesn't get anything past T1. Corse that's only viable if you're using fixed button slots
