In that case, your scenario is quite similar to mine.
I also moved from green to orange back in Feb.
Don't terminate your SH yet.
Signup for M1 first. Once you get the M1 ONT installed and confirmed internet is working, then you can bring your SH ONT to one of the service centres to terminate it (have to bring along power adapter, the yellow fibre cable, and the LAN cable that comes with the ONT). Cannot call to terminate, have to terminate by returning to the service centre.
If you are porting over your digital voice to M1, then don't terminate SH first. Wait for 5 working days after M1 ONT installed until your current number works on the M1 ONT, then you can terminate SH.