[Fire TV Android Development] Sus_i:
Yeah, ofcourse. You can do this on every gen1 box (bueller) or stick (montoya), regardless of the firmware OS. But you have to choose the right bootloader for your device, if you decide to flash a new system, bootloader, recovery... i.e. you can't flash an unlocked bootloader to a locked device, it wont start with the unlocked one.

Good news, its easy if you have a locked box thats working and on 5.2.7.0. You can skip any flashing and just do the rooting stuff... i.e. install bootmenu/twrp and root it:

#!/bin/sh

# This is my shared folder where I put backups and the zip files, i.e. usb stick...
UNLOCKED="yes"
SHARED="/home/locomex12/Desktop/Folder"

# Unzip rbox's prerooted zips to your $SHARED folder then set this to the location of that folder
# Get those here: https://xdaforums.com/fire-tv/development/prerooted-stock-images-t2882337
ZIP="${SHARED}/bueller-5.2.7.0-rooted_r1"

# Location where the backups of the CURRENT image on the fire tv will go before it's overwritten
BACKUP="${SHARED}/backup"

# Download here https://github.com/xpirt/sdat2img
# Then change this to the location of the python script
SDAT2IMG=~/Desktop/Folder/sdat2img.py

# This should be the same on most linux systems (tested on Kali linux)
DEVDIR="/dev/disk/by-partlabel"

# Where to mount the mmc partitions
MNT="/mnt/emmc"
SYSTEM=$MNT/system

# Back everything up JUST IN CASE...

DATE=`date +"%Y-%m-%d-%H%M"`

# echo "Backing up... "
mkdir -p $BACKUP/$DATE
echo -n "Unmounting system..."
umount $DEVDIR/system
echo "Done."
dd if=$DEVDIR/system | pv -s 805306368 | dd of=$BACKUP/$DATE/system.img
echo "Done."
echo -n "Unmounting recovery..."
umount $DEVDIR/recovery
echo "Done."
dd if=$DEVDIR/recovery | pv -s 9773056 | dd of=$BACKUP/$DATE/recovery.img
echo "Done."
echo -n "Unmounting boot..."
umount $DEVDIR/boot
echo "Done."
dd if=$DEVDIR/boot | pv -s 6627328 | dd of=$BACKUP/$DATE/boot.img
echo "Done."

echo -n "Clearing cache..."
umount $DEVDIR/cache
mkfs.ext4 $DEVDIR/cache
echo "Done."

# Mount system

echo "Mounting system..."
mkdir -p $SYSTEM
mount -o rw $DEVDIR/system $SYSTEM || exit 1
if [ ! -e "${SYSTEM}/xbin" ]; then
echo "ERROR: couldn't find /system/xbin - is the mount point correct?"
exit 1
fi

# Now copy stuff and root it

echo "Installing TWRP..."
cp -r $ZIP/recovery $SYSTEM
rm -f $SYSTEM/recovery/recovery.img
echo "Chmodding and chconing RECOVERY..."
chown -R 0:0 $SYSTEM/recovery
chmod -R 0755 $SYSTEM/recovery
chcon -R --reference=$SYSTEM/bin $SYSTEM/recovery

# Backing up e2fsck and symlinking it to 2ndinitstub...
mv -i $SYSTEM/bin/e2fsck $SYSTEM/bin/e2fsck.real
echo "Symlink e2fsck to 2ndinitstub..."
ln -sf ../recovery/2ndinitstub $SYSTEM/bin/e2fsck
chcon --reference=$SYSTEM/bin/e2fsck.real -h $SYSTEM/bin/e2fsck

echo "Installing SU..."

cp -f $ZIP/su/su $ZIP/su/supolicy $SYSTEM/xbin/
chown 0:2000 $SYSTEM/xbin/su $SYSTEM/xbin/supolicy
chmod 0755 $SYSTEM/xbin/su $SYSTEM/xbin/supolicy
chcon --reference=$SYSTEM/xbin/trapz $SYSTEM/xbin/su $SYSTEM/xbin/supolicy
ln -sf su $SYSTEM/xbin/daemonsu
chcon --reference=$SYSTEM/xbin/trapz -h $SYSTEM/xbin/daemonsu

cp $ZIP/su/libsupol.so $SYSTEM/lib/
chmod 0644 $SYSTEM/lib/libsupol.so
chown 0:0 $SYSTEM/lib/libsupol.so
chcon --reference=$SYSTEM/lib/libsuspend.so $SYSTEM/lib/libsupol.so

cp -r $ZIP/su/SuperSU $SYSTEM/app/
chown -R 0:0 $SYSTEM/app/SuperSU
chmod -R 0755 $SYSTEM/app/SuperSU
chcon --reference=$SYSTEM/app/Bluetooth -R $SYSTEM/app/SuperSU

echo "Unmounting system..."
umount $SYSTEM

echo "Done"

You can use this script for a working & locked bueller device (all previously unrooted FTVs with that high OS number are locked). I deleted the flashing thing for you, same path as before. Paste this into a txt file in your Folder on Desktop, rename it to locked.sh. Be sure that you have the unzipped rbox rom as usual in this Folder. Do the dos2unix and chmod thing. It does a backup before rooting, in case something gets wrong. Have fun... :D :good:

Edit: fixed typo ^^