$SkillRestriction[skill] = $SkillA @ " 15 " @ $SkillB @ " 25";
They already have things like that...cept it's more like skill and remort or level, but you could do it like that (although i haven't tested it).
I'm thinkin' of doin' something like that if we can add in $SkillLore as skill 19 (the one after endruance that says no longer used). It'd be a bard thing, as they have no primary skills fitting to their class. You could then have bardic magic that would rely on Ncast and lore...something like
$SkillRestriction[enchantitem] = $SkillNeutralCasting @ " 200 " @ $SkillLore @ " 800";