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Depending the hardware this will be possible. 
If you have created a proper backup with the AutoBackup plugin with AutoInstall on and didn’t install any plugins outside the feed, your box will be up-and-running within 4-8 minutes depending the speed of your box. Sometimes I perform this scenario several times a week with my Ultimo 4K.

But beware that the 6 series will stop being maintained shortly.

It may be interesting to share your considerations to go back to such an old version, maybe it's something we can fix. Unless it's due to a closed source CAM, then we can't fix it.