Okay, I did this:
1) Created a new Windows 10 administrator account.
2) Switched to that account.
3) Noted that the WB icon wasn't in the system tray.
4) Noted that windows weren't skinned.
5) Found that WB was in the Start Menu, so I ran it.
6) Noted that most of the installed skins weren't available. Chose one that was, but after loading it, it didn't apply.
7) Ran the Purge_WB.bat script.
8) Tried to reinstall WB, but was halted by the error "Setup can not create the following folder: C:\Users\Public\Documents\Stardock\Windowblinds\Diamond", after which the setup aborted.
9) Switched back to my normal Windows 10 user account, successfully reinstalled WB; rebooted.
10) Switched to the new Windows 10 account.
11) Noted that the WB icon wasn't in the system tray.
12) Noted that windows weren't skinned.
13) Found that WB was in the Start Menu, so I ran it.
14) Noted that there were only a few of the usual skins available; loaded the Win8 skin...successfully!
15) Switched back to my normal Windows 10 user account.
16) Noted that the WB icon wasn't in the system tray.
17) Noted that windows weren't skinned.
18) Found that WB was in the Start Menu, so I ran it.
19) Noted that all the usual skins were available. Loaded the Lantana 2 skin; it didn't apply.
20) Tried loading the Win8 skin...and it worked!
21) Again tried loading the Lantana 2 skin, but this time nothing happened when I clicked the "Apply style to desktop" button. Restarted the WB program; the button still doesn't work.
22) Noted that the WB icon was now in the system tray.
So I've managed to replace the ugly Windows 10 style...but why can I no longer access the Lantana skin?