Do you want the hat to stick with just an illusion, or would Alter Self work? Lycanthropy does not change your type, just adds the shapechanger subtype, so Alter Self should work. In which case, the hat would cost 6x the amount (lv 2 spell, lv 3 caster vs 1 & 1 for Disguise, same durations on the spells). Glamered clothing would cover the outfit appearance, as mentioned before, which works well because Alter Self does not affect your gear.
I can't see why it wouldn't work. Let's see, a continuous effect, level 1 spell, CL 1 required to cast it, duration of 1 day/lv... +1,000gp to the cost of the item. I would put a limit on what items you could affect with this, so that only items with completely passive effects could be permanently enchanted with it, due to needing to make a will save just to be able to use Identify or the like to figure out how to activate it, which a caster is only allowed to make once, could be problematic.