Yes, AllSpecials.xsd has the definitions for active perks. If I wanted to duplicate the effects of a passive skill - for example create an active perk called Concentrate_1, and give it the effect of Criticals_3 (an existing passive perk) - I don't think that's possible because nowhere in AllSpecials.xsd is there provision for critical hits.

I'm somewhat sure I can figure out how to mod the various passive perk, but active skills are out of my reach due to the XML schema limitations.