this was posted in the official lenovo forum by an mod. (translated from Russian)
"No. This is the official firmware, which is sewn without unlocking the bootloader."
and
"Select flashall.xml - this version of the firmware will save the user data in your device"(using rdslite)
kindly confirm
mentioned "Flashall.xml", uses "fastboot flash" commands. I dont think these commands will run on a locked bootloader. You'll have to unlock it & that will erase all userdata.
Though, once bootloader is unlocked you can skip "fastboot erase userdata" to avoid loosing your data
Other option to save userdata is "adb sideload"- but that requires suitable OTA zip file. This N ROM zip file cant be sideloaded on the soak N build.
Hope your confusion is cleared ?