Rangers as well as other teams, will be allowed to sell a season ticket for home games.
If you're a season ticket holder for next season, I would imagine Rangers will deduct the cost from the money you've paid for a physical season ticket. What options Rangers put forward for the remainder of your cash will be interesting. Although the idea of using that money for your next season ticket might seem like a good idea, we usually use season ticket revenue for running costs etc, so we'll more than likely already spend it throughout season 20/21.
I'm sure Rangers will confirm what options you have shortly.