I think the issue you run in to is more entire version numbers. For instance, if you were trying to restore from 9.1 on a device running 8.1 that'd be an issue.My backup is on 9.1. If I downgrade to 9.0.2 and try and restore from my 9.1 backup, will it work or will it tell me my backup is not compatible? Would love to jailbreak but don't want to lose my backup.
just download the 9.0.2 firmware and then plug your iphone into ur computer
go to itunes hold shift and press UPDATE then select the 9.0.2 firmware and everything will still be there on your phone
without making a backup and restoring it!
I did this yesterday and it worked fine