Seeing as how I'm starting to hate 18.10 more and more, I've decided on a downgrade.
Also seeing as how a downgrade is not really recommended and I'll have to probably go with a total reinstall, what's the optimal way for me to keep my data and only have the live-USB touch the OS and its related files only?
Think "soft" reinstall.
Sorry that 18.10 is not working out for you.
Reinstalling an OS is inherently risky.
While the Ubuntu installer will TRY to preserve your data, it might fail.
This venue is littered with folks who did not read the options carefully, or who misunderstood the options offered, or who had a power loss, discovered a bug, suffered a hardware failure, had a cat-on-keyboard, etc.
If your data is valuable to you, then preserve it.
It's never failed me, but I always back up all data anyway.