[Moto G4 Plus Questions & Answers] echo92:
I don't know if you'll be able to revert back to your old 6.0.1 TWRP backup once you've updated to Nougat, as the modem and other firmware would be newer than 6.0.1. Additionally, if you've updated to the June update, be very careful about downgrading by flashing a stock ROM as the bootloader has been updated in this update, and attempts to downgrade the bootloader and GPT seem to result in bricking of devices (though TWRP flashes do not care about the bootloader and GPT usually, so you may be okay in that regard).

As for the procedure for updating, you do not have to re-lock your bootloader if you desire root later. Bootloader lock status does not appear to affect OTA updates/installations - only the presence of a non-stock recovery, system or kernel will cause the update to abort. Re-locking for your purpose, unless you're wanting to send your device for service or to sell it, is unnecessary so leave it unlocked. The unlocking instructions in the guide are only there if you're coming from a device with a locked bootloader. If you're going down the OTA route, a general guide would be:

1)Unroot your root manager (following the root manager's uninstall instructions).

2)Flash a stock recovery (and stock kernel) from a stock ROM. Ensure the stock ROM you're using is the same build as what you're currently on. If you've flashed a custom logo.bin to hide the bootloader warning, you'll need a stock logo.bin.

3)Download and flash the OTA update in your stock recovery (should happen automatically).

4)Reboot into Nougat NPJ25.93-14.

5)Accept and download the March update, repeat the install.

6)Accept the June update if it's arrived for you (I've only seen the June update deployed in Brazil and India at the moment, other territories may have to wait), or download and flash the OTA update in stock recovery. The June security patch appears to only flash over the March update.

7)Once you're updated, flash TWRP and back up your entire system again (you may wish to flash a newer TWRP).

8)Flash ElementalX and your root manager as directed in the guides. Ensure the root manager you flash is quite recent - either SuperSU 2.79 SR3 or newer (2.82 SR1 is the latest) or magisk v12 or newer should be okay.

NOTE - you could skip steps 1-5 if you use fastboot and the commands in my previous post with the March 2017 fastboot ROM. You'll be flashing stock copies of the partitions to your device and bring it up to the March 2017 update in one go.

With 6.0.1, you could root after you flashed TWRP - on stock Nougat, the anti-rooting security is much stricter, and attempts to root with the stock (i.e. Motorola, hudsoncm) kernel may cause your device to bootloop. Thus, to get around those security measures, we can flash a custom kernel (i.e. a 3rd party kernel) that doesn't have that security. We have ElementalX v1.04 https://xdaforums.com/moto-g4-plus/development/kernel-elementalx-g4-0-01-t3424836 and vegito v6.08 https://xdaforums.com/moto-g4-plus/development/kernel-vegito-kernel-1-0-13-september-t3461021 as custom kernels. To flash a custom kernel:

Download the stock version of the kernel (the LineageOS versions are for Lineage-based custom ROMs).

Reboot to TWRP.

Backup your boot partition (this contains your stock kernel)

Go back to 'Install' and tap the kernel zip

Follow the installer instructions to flash (e.g. with ElementalX, I've got stock 1561 MHz, no double tap to wake and none of the options selected on the installer screens).

Wipe cache/Dalvik

Reboot.

After flashing the custom kernel, then you can proceed to rooting on a Moto G4/Plus.