Here's my experience with the v10 install. I had a fresh TimeMachine just in case, but I was lazy and didn't do a CCC backup...
I'm currently running Logic 9.1.8 and LPX.4.1 in Mac O/S 10.12.6. I had Waves v9.3 installed so that I can use my Waves plugins in both Logic versions. I also have a mix of plugins that are still in WUP and some that are not.
1) I upgraded the licenses for the WUP eligible plugins to v10 via the Waves website
2) I installed the latest version of Waves Central
3) Moved the new v10 licenses to my local machine via Waves Central. FYI - the old v9 licenses had disappeared from the local list. I now have a mix of v9 and v10 licenses. Note that the v10 licenses will authorize v9 plugins.
4) Installed 2 plugins/bundles that are not part of the v9.3 installer (they were released after 9/10/2015) via Waves Central. These are now at v.10 and only work in LPX.
5) Downloaded the offline installer for v9.3 (https://www.waves.com/support/run-waves ... on-logic-9
6) Installed the v9 plugins that I wanted to be accessible in both version of logic - making sure not to install the 2 that were v10 only (I couldn't since they weren't an option, but if you do have overlaps, make sure to only have one version installed).
7) Tested in both versions of Logic just to be sure!
I'd assume that if you are happy with the v9 versions that you are currently running then all you need to do is steps 1-3. That'll give you the v10 versions in case some nice updates come along, but still let you run v9.
Obviously, this isn't going as smoothly for others, but maybe this will help......