Hi there, unforunately I didn't tested it for webGL as my main development environment is windows based, but I think that it should work just fine for webGL too. I will test it for webGL and will provide you further information regarding webGL.
For editing the script , you need to go to your CopperCube extensions directory generally located at Documents/Coppercube/extensions/
and look for "behavior_Character_selection.js" file and then you need to open it in (VS Code) so that you can edit it as per your requirements.
Thanks for the purchase :) Glad that you like it. :)