Once you unequip a piece of your "blessed" gear, you lose that particular item's magic find buff until you revisit the friendly NPC. This would make logical sense--switching a few rings to LoH would only net you a loss of about 30-40 mf for a reflect damage pack -- returning to town doesn't take incredibly too long anyway, just be sure to make these NPCs closely available to the waypoints.
I think this would add a layer of role playing that feels like it is aligned with the lore of the game too. You wouldn't just be mindlessly slaying monsters for gear to sell for american dollars, you would be seeking out the blessing of Sanctuary's holy men to seek out and destroy the menacing demons.
This way, a player can receive FULL mf bonus on his items immediately when he or she wants to go adventuring instead of having to wait for a cooldown timer. It also doesn't punish a player by making that player lose ALL mf for switching a few necessary survival items.
I would appreciate any constructive criticism as I wanted to create a more friendly mechanic than what has currently been postulated by the diablo developers.