Let's start with the usual formula: you are the only one responsible for what you do with your device. If you do what follows, without any doubt you will brick your device. And you will be sad. Most likely you will cry. And no one will help you. Well, at least for sure I won't. The only think I can advice you: DO NOT DO THIS.
Now that you know what kind future awaits you, here are some steps (most likely incomplete and incorrect) that will give you hope to root Boyue ereader, but eventually will prove to you that you shouldn't have done this:
(*) - you can also take a look at this script (I didn't use exactly this script to root my Ares, but the one I used was similar):
PREFIX=parent_directory_of_mounted_system
set_perm() { chown $2:$3 $1 || exit 1 chmod $4 $1 || exit 1
}
mkdir_perm() { mkdir -p $1 || exit 1 set_perm $1 $2 $3 $4
}
cp_perm() { cp $1 $2 || exit 1 set_perm $2 $3 $4 $5
}
mv_perm() { mv $1 $2 || exit 1 set_perm $2 $3 $4 $5
}
mkdir_perm "${PREFIX}/system/app/SuperSU" 0 0 0755
mkdir_perm "${PREFIX}/system/bin/.ext" 0 0 0777
cp_perm common/Superuser.apk "${PREFIX}/system/app/SuperSU/SuperSU.apk" 0 0 0644
cp_perm common/install-recovery.sh "${PREFIX}/system/etc/install-recovery.sh" 0 0 0755
cp_perm arm64/su "${PREFIX}/system/xbin/su" 0 0 0755
cp_perm arm64/su "${PREFIX}/system/bin/.ext/.su" 0 0 0755
cp_perm arm64/su "${PREFIX}/system/xbin/daemonsu" 0 0 0755
cp_perm arm64/supolicy "${PREFIX}/system/xbin/supolicy" 0 0 0755
cp_perm arm64/libsupol.so "${PREFIX}/system/lib64/libsupol.so" 0 0 0644
cp_perm "${PREFIX}/system/bin/app_process64" "${PREFIX}/system/bin/app_process64_original" 0 2000 0755
mv_perm "${PREFIX}/system/bin/app_process64" "${PREFIX}/system/bin/app_process_init" 0 2000 0755
mv "${PREFIX}/system/bin/install-recovery.sh" "${PREFIX}/system/bin/install-recovery_original.sh" || exit 1
rm "${PREFIX}/system/bin/app_process" || exit 1
ln -s /system/etc/install-recovery.sh "${PREFIX}/system/bin/install-recovery.sh" || exit 1
ln -s /system/xbin/daemonsu "${PREFIX}/system/bin/app_process" || exit 1
ln -s /system/xbin/daemonsu "${PREFIX}/system/bin/app_process64" || exit 1
# After installation, run '/system/xbin/su --install', which may need to
# perform some additional installation steps.
You probably need to modify boot.img, add an oneshot service that starts daemonsu on a valid selinux context. From 4.2 onwards installing /system/xbin/su isn't enough to get a root shell.
I can confirm the script you put together works and persists between factory resets on my newly bought BoYue LemonRead S62A.