I wanted to offer a follow-up to contribute to the knowledge base.
I was able to remove and re-flow the soldered pads on the Main Relay in
the subject auto. In fact, I was able to remove it without need of
removing any trim panels. (Side note here. As Principal Skinner's
mother Agnes commented about Seymour, "He has the tiny hands of a chimp".)
The operation was a success and the patient survived. Now I will see if
the problem recurs...
As to soldering, just keep the iron tip clean by wiping with a moistened
cloth after each 4 or 5 pads. I used a bit of 60-40 rosin-core solder
and melted against each pad to help conduct the heat and have a little
more solder to flow around the joint.
The mount point has a tab that helps to hold the relay on the bracket at
reinstall time. It was a bit risky that if I dropped the bolt, the left
foot well side panel would have required removal.
So, thanks to TeGGeR@ and all the others who responded.