Downloaded the 1.3 patch, attempted to install. Got error message in the patch log, which states

Baldur's Gate II - Enhanced Edition patch log
Update from version 2.0.0.1 to 2.0.1.2

Incorrect version of: C:\Games\Baldur's Gate II - Enhanced Edition\chitin.key
Incorrect version of: C:\Games\Baldur's Gate II - Enhanced Edition\lang\en_US\dialog.tlk

I know one of my mods is responsible for changing these files, but I don't know which one. I've heard rumours about this game, that compared to classic BG2, it is more mod-unfriendly with every patch update. How can I fix this? Is there an alternative to uninstalling all of my mods, installing the patch, then re-installing my mods? Would that even fix the problem, or make it worse? Beamdog made a pretty good game, but woe betide you if you have any thoughts of modifying it. Please let me know what I can do. Thanks guys.

They're not rumours, it's fact. And since the patch needs to replace those altered files, other than uninstalling/reinstalling your mods, there is nothing you can do, except don't install the patch until you are ready to start a new game, and reinstall your mods.