My current iPhone isn’t jailbroken, and when I did have a jail broken phone, I never tried to revert to an old version of an app, so I’m honestly not sure.
Im also not sure about exempting an app, although I’d like to find out about this, too, depending what happens in mid-January. It’s unclear whether person detection will continue to work if you stay on old versions, but if it will, I may opt to do that