For world R5, I actually saw this idea in the IWL discord that I might try to implement one day. If you get close to a positive cost Peach door, all keys except for Pure and Stone get turned into Peach keys. A negative cost Peach Door turns them back. Converted Peach keys only count for cost and are never spent, so if you have 3 White, 3 Orange, and 0 Peach keys, convert them to Peach keys, spend 3 Peach keys, and turn them back, you'll still have 3 White and Orange keys and you'll have -3 Peach keys.