Changing a PlusPoints flight without having to call

This one definitely falls under the category of "if I don't make a note to myself right now, I'm going to immediately forget how to do this next time."

It's a super-specific problem: 

• I have a flight leg with a confirmed 40 PlusPoint upgrade into Polaris. 
• I need to change this leg to a different day/time. 
• I know that my new flight has PlusPoints ✅ instant-upgrade seats available. (I used Seats.aero and then manually verified the availability on United.com)
• I'm using United.com to change my flight and the search results only show me one option: a deeply-discounted fare + 80 PlusPoints to upgrade
• I would prefer an option with a less-discounted fare that only requires 40 PlusPoints
• I would prefer not to call United to have them sort this out. (In my case, the Australian United phone center is only open normal business hours, not 24/7)

The solution:

• Change the flight on United.com (from a desktop browser) and manually set the 'Search by Fare class' field to: W (FYI: a bug/change on United.com now prevents you from putting in a comma-separated list of fare classes. You have to try the 40-point-upgradeable fare buckets one at a time. W is the cheapest, then V, Q, H, U, and E.)
• The resulting search results will now have a new column called "Requested Fare Class" that will only show fares that are upgradeable with 40 PlusPoints versus 80.
• After the new ticket is issued, use the Upgrade Cabin button in the My Flights view to apply the PlusPoints to the new trip