As title says ?

new forge categories will probably never be possible (without hacking) as it requires bethesda to sublicense ScaleForm software (3rd party licensed software) in order to edit them.

How bout perk trees ? They added 2 new ones in dawnguard so is perhaps unhardcoded now?

well keep in mind they are using Scaleform, so they can add whatever they want to the UI. we don't officially have the scaleform source files (and probably never will)

As it stands we cant add perk trees, as already mentioned. The new ones are in the CK now to.

We can add new perks, which I've done in my hunting mod.

Maybe you can just add your perks to current relevant trees like me