Party members are PCs, playable characters, not NPCs. You have some control of them, if not as much as you have with party members in a Final Fantasy. Merlin is an NPC. So is Leon, with no battle controls. So were the unnamed characters hanging around Traverse Town in KH, which are more typical of how "NPCs" are defined.
Regardless, good luck with making party members dance to your tune in KH2, if you decide to play. PCs do what they do, with a nudge through Customization. FWIW, never could turn them into solitary fightin' machines in KH2. Can't see hacking doing much, whether to good or amusing effect.
Guides and other contributions: http://www.esque.com/slr/gamefaqs/ FFX, FFXII, KH, KH Re:CoM, KH2, Okage: Shadow King, Secret Agent Clank