Theoretically yes:
All Swiss Rail tickets (for this route) are also valid on the GEX. However, a seat reservation is mandatory on this train.
You can get off freely, but to get back on you need a new seat reservation for the GEX. Of course, you can also take another train that does not require a reservation.
The tickets you buy for the GEX have the reservation included.
If you buy a ticket for another train on this route, the reservation is not included, but this supplement can be purchased later without any problems, provided that there are still seats available.