Here's an idea:
If they make Peter Sam and Sir Handel, then they should package with them a set of alternate nameplates, held onto the sides of the saddletanks by magnets (not sure if that would interfere with the motor, though), of their ex-Mid-Sodor monikers, Stewart and Falcon.
Likewise they could package an alternate funnel for Peter Sam, so people can alternate between Peter Sam's original funnel and his Giesel funnel.
If they make Peter Sam and Sir Handel, then they should package with them a set of alternate nameplates, held onto the sides of the saddletanks by magnets (not sure if that would interfere with the motor, though), of their ex-Mid-Sodor monikers, Stewart and Falcon.
Likewise they could package an alternate funnel for Peter Sam, so people can alternate between Peter Sam's original funnel and his Giesel funnel.