[NOOK Tablet 7" ROMs, Kernels, Recoveries, & Other ] turtleletortue:
Things to know:

This is for the 7" with 16GB of storage and Android Oreo Go, I don't have the other 7" to test, it probably won't work or will brick the marshmallow model. The BNTV460 has the codename of "st18c7bnn," so that's why the repository is named as such.

USING THIS WILL VOID YOUR WARRANTY. THERE IS ALWAYS A CHANCE OF BRICKING YOUR DEVICE WHEN MODIFYING IT.

You will need your bootloader to be unlocked before this.

The stock rom will revert this to stock recovery every time you boot into the stock rom, so it's recommended to use this and immediately install a custom rom or GSI afterwards.

Here is a link to the device tree for building it if needed. https://github.com/turtleletortue/android_twrp_bn_st18c7bnn

Download this TWRP image: https://androidfilehost.com/?fid=8889791610682945941

Installation:

0.5. Back up important data and charge device to 100%.

0.75. Take a backup of the stock rom using mtk-su & dd or using wwr-mtk.

1. Boot into android. This device must be the Nook Tablet 7" with Android Oreo Go edition.

2. Enable developer options, and then turn on usb debugging.

3. Go into an adb shell with the device, and confirm the usb debugging dialogue on the device. If you get a permissions error, drop down the notification menu and change device to using usb for file transfer.

4. Confirm that the name on the shell is st18c7bnn, and not st16c7bnn. If the name is st16c7bnn, do not continue with this guide.

5. Exit out of the shell, and then type in "adb reboot recovery"

YOU WILL LOSE ALL OF YOUR DATA ON STEP 6, this is necessary for GSIs or for custom roms.

6. Once in the stock recovery, use the volume keys to navigate to wipe data/factory reset and use the power button to select it. Then select yes.

7. Once done, use the volume keys to navigate to reboot to bootloader and confirm with the power button.

8. Once the device says fastboot mode, navigate to the directory of the recovery and type in "fastboot flash recovery twrp-st18c7bnn-3.4.0.0.img"

9. If successful, type in "fastboot oem reboot-recovery"

10. Device should now boot into TWRP, swipe to allow modifications.

11. You are now in TWRP. There are two paths to go to.

Path 1: Custom Rom

1. Click Advanced -> ADB Sideload

2. Plug into your computer, and use adb sideload "location of custom rom zip".

2.5. If you want Google Play, install appropriate opengapps for your Android version. Use adb sideload also.

Gapps from https://opengapps.org/ should be arm, pico.

3. If you encounter errors, alert the developer.

4. Go to power -> power off.

5. Turn on device. Once the LineageOS logo (or whatever custom rom you use) appears, you can relax and plug in the device while you wait for it to boot up.

Path 2: GSI

1. Download a GSI. Recommended config is as of writing: AOSP 9, arm a-only. Make sure to extract it so that it is an img file.

2. adb push "location of gsisystem.img" /sdcard

3. In TWRP, go to install -> install image and then select the GSI image, and select System Image and flash.

4. Flashing can take a while to occur, so plug in the device and wait.

5. Once done, go into advanced -> file manager. Navigate to /sdcard and delete the GSI image.

6. Go to power -> power off.

6. Turn on device. Once it reaches the android logo you can relax now. Plug in the device and wait for the GSI to boot.