For old kit mods (classic game), it is very easy to play with kits unusability flags as long as you follow good rules (for example, your kit can't wear leather armors, add the shapeshiper flag to your kit flag, your kit can't use use daggers, add one of the cleric kit flag...) and it won't screw up all other kit mods. And DON'T FORGET to never use this flag in EE games. As far as I saw, it is not a good idea.