1) You can't.
See here. The load game error has to do with lua modifications breaking when reloaded and the mod disables it because it would just cause a crash anyway to try to load a game from the in-game menu. It's a vanilla bug caused by modding anything significantly.
2) There aren't that many renames, but with just CivUp at least they shouldn't be changing the essential function of the buildings/units renamed. I would consider most of them to be effectively UI improvements anyway as they're just cosmetic. They are listed in GEM documentation on the wiki page you linked where they are often accompanied by non-cosmetic changes like building or unit stats, but if you're just using CivUp, none of that matters. It just renames the thing.
This is a partial list of renames (there are other features that are renamed aside from buildings and units, like unique civ abilities or happiness descriptors).
a) Blast Furnace - was Forge
b) Dragoon - was Cavalry
c) Chang Suek - was Naresuans Elephant
d) Arquebusier - was Musket
e) Musketman - was Rifleman
f) Rifleman - was Great War Infantry
g) Missile Sub - was Nuclear Sub
h) Chinampa - was Floating Gardens
i) Smithy - was Workshop
j) Workshop - was Windmill
k) Foundry - was Iron Works
You can disable or modify these changes by editing the core.sql file in the text bark folder of CivUp.