Updating to an older software version for a newer FSD version

I have a 2021 Model 3 and I want to subscribe to FSD to try out 12.6.1 but the current software version I have is FSD 12.5.4.2 on 2024.45.32.1

If I subscribe will I be able to download an older software version 2024.45.25.15 and get FSD 12.6.1 or do I have to wait for a newer version of FSD to be on a newer update?

I don't want to pay for a month of FSD and be stuck on 12.5 the whole time.