My parents have an award booking from dad's MileagePlus account - I have the record locator and can go in to the reservation. I would like to pay to upgrade them to First without dad getting a notification e-mail right away. There is an option to change the e-mail address under traveler contact information. 1) Would changing the contact e-mail to my own issue anything to the original (dad's) e-mail address? 2) Assuming no, if I upgraded the itinerary after changing the e-mail address, would there be any notification sent to him since the original ticket was booked from his MileagePlus account?

This will be the final flight home after an ultra-long-haul international flight and it would be nice for them to have that last leg in first. They don't quite understand how exhausted they'll be at that point and how much they'll appreciate it, so finding out now would spoil the surprise and they would be more upset about me being wasteful and paying the (admittedly high) cost of the upgrade.