Hello,
Theoretically it would be possible. You can have separate RSTP at each site with their own root bridges.
You might disable RSTP, enable IGMP snooping, Disable PVST etc. on links facing the provider devices.
However you would need to take great precautions as any loop has a potential to affect multiple sites.
Note:- I have not seen anybody doing this though.
Regards,
Rushi