I defined it as a standalone mission to make it easy to test. It should make it easier to include it in other missions, too.
If you're interested in checking it out, I spent a few hours documenting how it works and how it's put together in these Wiki pages. (https://gitlab.com/jpssgtrock/mpmissions/-/wikis/Role%20Selection%20Template) The GitLab page for the mission itself is here (https://gitlab.com/jpssgtrock/mpmissions/-/tree/master/Role-selection-template.VR). Or you can just grab the whole thing as a zipfile (https://gitlab.com/jpssgtrock/mpmissions/-/archive/master/mpmissions-master.zip?path=Role-selection-template.VR). ;)