For MR8300 (dual firmware) . Sysupgrade instead Factory Image file. Do you think it can work?

Guys I have a Linksys MR8300 and I am quite happy with it. Quad core with 512mb of Ram allows you to do many things even on more complex networks. This router has dual firmware so that if in case of incorrect load it starts with the other flash. I have installed the "advandec rebbot" package which allows you to select which firmware can be rebooted with. Now my question is about the update. Assuming you want to update without reinstalling the ROM from scratch, my idea would be to restart the router with the original firmware and on the other hand load the Sysupgrade instead of the Factory Image file. Do you think it can work? Thank you.

No, you need the OpenWrt factory image when flashing from stock, you can build your own image with all your packages though, it's not very difficult once you find your way around the menuconfig.

edit - you can use the online image builder too if you know all the packages you want, it's even easier.

Image builder is surely useful,but all the settings must be exported before or will be lost. A this point the package update it is simpler even not same operation.

I also have a MR8300 which I run under snapshots. I flash it a couple of times a week. I also reboot to linksys firmware using advanced reboot before flashing. And restoring the settings after flashing is not such a big deal. Furthermore you can include them directly in the image.

as you said normally does not a big deal if you have standard con figuration. I my case i use some additional packages that increase the operation complexity. So is needed to backup additional packages as well as the settings. In this case the restoring may be a little bit risky. To avoid this risk may be needed a command (or procedure) to backup both additional packages and and the whole settings (for included and not included packages) .

Those settings are in /etc ?
You can manually specify what to backup in Luci : backup/flash, configuration
I have never tested this though.