You can follow these next steps to downgrade from version 10.0.x to version 9.3.x:
IMPORTANT: This procedure will only change the VW software. Rest of the components like WO will still be running with 9.3.x build specifics.
1) On MCN (currently running with 10.0.x) navigate to:
Configuration >> System Maintenance >> Update Software >> Re-image Virtual WAN Appliance Software (It is just the software re-image from UI and not the factory reset process)
2) Upload the MCN hardware specific .tar file for release 9.3.x build and proceed with the installation (re-image). This step will clear the configuration from the appliance.
3) In the config editor, import the backed-up config from 9.3.x release and proceed with the staging and activation on MCN.
4) Perform Local Change Management for each branch.