sorted btw. I created a .slangp file for each game (using a script). Happy to share the script and/or .slangp files with anyone else who stumbles on this issue.
Unfortunately, installing 2 instances of Retroarch (one main install, and one for the Bezel Project download then copying the downloaded overlay folder with .png and .cfg files to the main install) didn’t work, and I had to keep reapplying the shader, even after setting a core default.
Fantastic work though, your shaders look absolutely fantastic when paired with TBP