WetGeek plan to install Solus as soon as it (the new SSD) arrives
Mission accomplished, and it was easy to modify the BIOS to allow selecting the boot drive, as in the "a couple of pointers ..." in my message, above. Now we're back to seven machines in this house running Solus, including six Budgie and one MATE.
If anyone's counting, you may have noticed that I missed a day. I had an adventure pulling unwanted vines from the wild blackberries along our private road. I disconnected a few large non-fruiting vines by snipping them near the roots, grabbed a bundle of them, and pulled them away from the bushes. I had to pull really hard, and when they suddenly let go, I ended up face down in the gravel road. I wasn't in any condition to deal with eleven tiny screws that day.
This morning, though, with a little help from some ibuprofen, I could handle them. Configuring the BIOS, removing the laptop's bottom cover, and replacing the SSD and the bottom cover only took about 10 minutes. After that, it was a very ordinary Solus Budgie installation. (I.e., very fast and easy.)
I installed 402 upgrades, installed some software, did a bunch of configuring, and did a backup. She'll be happy now, and I think she's much safer on Linux than Windows 10. Altogether, it was well worth the effort!