AngelCAD is not a "another CAD Exchange format". It is a scripting tool that creates existing standard formats such as STL, OBJ, OFF, DXF, SVG and more. It also reads some of those exchange formats. There is no new exchange format.
I guess the .xcsg format is part of xcsg rather than AngelCAD, and the xcsg README.md doesn't mention being able to write out .xcgs files. Most CAD systems allow you to make multiple changes to a design, I don't see that with this system.
You could have done scripting for STEP models.