Thanks for the replies. Yeah, I did overthink this a little. I actually cringed at the thought of coming back to this thread and getting flamed.
Reading
this thread: https://www.bikeforums.net/classic-vintage/591501-10-speeds-126mm-hub-success.html is what got my thinking a little convoluted. Your responses created a good sanity check.
I'll be putting the wheel for sale up on Craig's List with an eye on swapping the rims when next I have downtime if I don't get any reasonable response or if I might find another old bike needing a rear wheel.
I did goof up on the numbers in my original post going by memory instead of double-checking. Sleep deprivation never helps.
The Ryde Sputnik does have a published ERD of 600mm. According to the spocalc Excel spreadsheet that's floating around, the Mavic CXP-10 has two ERDs indicated, one of 600mm and another of 601mm.
Might an ERD difference of 1mm still be a problem for a rim swap?