I just tested it with @ChunkyPotato , and yes, it’s possible!
Unlike what it says officially on STM or ARTM’s page, you can take the metro multiple separate times in a single trip, as long as it’s within 2 hours.
Metro > Metro = NO
Metro > Bus > Metro = YES
Metro > REM > Metro = YES
Metro > REM > Metro > Bus > Metro = YES
It’s even possible to transfer to the same station with a single ticket.
Ex: Tap at the station, then exit. Tap on a bus, and exit, tap at the same station, it works. As long as it’s after 5 minutes tapping the metro station, you can do it in 1 ride.