Will they ban you for the reshader mods on GTA Online?
Potentially yes. I got a short term violation for it ( well I'm guessing it was for reshade and sweetfx because it was the only thing I was using for online. Didn't actually think there would be a problem with a visual mod that doesn't actually alter any gameplay or game files.
My single player was hugely modified, but they should have only been triggering for single player as I was using OpenIV which separates online and offline completely. But who knows, maybe it didn't and a proper single player mod got activated accidentally when I entered online mode.
Long and short, any Rockstar game I play now online I play it totally vanilla.