Welcome to TWC, Denroaspis!
First, what mod did you installed and second have you deleted the script folder, located in -
C:\Users\<username>\AppData\Roaming\The Creative Assembly\Empire\scripts
Delete the script folder (I bolded in blue) then reinstall ETW and only launch it before installing any mod, just to see if it's working. Also, feel free to come back ask for our help, should you need more help.
To my knowledge a mod manager for ETW doesn't exist, expect for the PackFile Manager (PFM) of course, but I wouldn't consider PFM a mod manager.
Most mods are mod foldered, which means that all vanilla files will be intact and that's the purpose for mods to be mod foldered.