I tried selecting the button in the customize ribbon dialog and picked Macro from the drop-down followed by clicking Browse.
It defaults to the Training folder.
A quick test yielded:
"C:\Users\Jason\AppData\Roaming\Unigraphics Solutions\Solid Edge\Version 108\Customization\New Theme 1\New Theme 1-QATCustom.xml"
It may be possible to get to it via the API but I haven't had a chance to look yet.