It's pretty simple. What you want to do is create a new preset: "Manage Preset" > "New".
Go into GC's present, and right click the "beats" row, and click "Copy JSON to clipboard".
Click manage preset, and disable GC's preset temporarily so you don't get confused. Go into your newly created preset, and right-click and paste JSON to clipboard.
Double click that, and rename "Connect to Beats" to whatever headphone you have so you know that it's for that brand.
Towards the bottom of the script, look for this line:
if item i of btInfo contains "Beats" and item i of btInfo contains ", 1" then
You want to change "Beats" to the BT name of your device that you see in the BT setting on MacOS.
If you click on appearance and settings, you can drag and drop a glyph (google image search) in the "icon" window or single click the icon window to scroll through a bunch of glyphs.
I'm still a bit unsure on how to get the preset to appear in GC-BTT settings (if I want to enable/disable it), but it doesn't make a difference for me since I always keep it on the main TB.
And then obviously, go back and re-enable GC.