This community may be more oriented towards the OpenSCAD port, gridfinity rebuilt: https://github.com/kennetek/gridfinity-rebuilt-openscad
The fusion 360 source files from the original project are a little jank when it comes to making customizations given AFAIK how fusion 360 operates. The port I've linked is much simpler to use when it comes to producing STLs for your own customized bins.