[Chromebooks] Nolirum:
Depends what you want to flash, probably.

You might be able to rewrite the relevant edify commands in the update-binary that you want to flash into an equivalent shell script for the Chrome OS shell.

However, by default the Android rootfs container is in a read-only squashfs format, so normally cannot be modified directly. One way to modify it is to make a writable copy of the container in /usr/local, then replace the original file pathname with a symbolic link to the R/W copy. This works fine for the most part (but does takes up extra disk space, and needs to be re-done after an OS update).

For instance, here is part of the rooting script mentioned upthread, which makes a writable copy of the Android container, copies the files from the original container therein, renames the original to .bk, replaces the original file pathname with a symlink to the copy and, at the end, changes a couple of relevant envs in CrOS's /etc/init/arc-setup-env file.

#!/bin/sh

# Detect CPU architecture

case "$ARCH" in
x86 | i?86) ANDROID_ARCH="x86";;
x86_64 | amd64) ANDROID_ARCH="x86";;
armel) ANDROID_ARCH="armel";;
arm64 | aarch64) ANDROID_ARCH="armv7";;
arm*) ANDROID_ARCH="armv7";;
*) error 2 "Invalid architecture '$ARCH'.";;
esac

# Make some working dirs

mkdir -p /usr/local/Android_Images
mkdir -p /usr/local/Android_Images/Mounted
mkdir -p /usr/local/Android_Images/Original

# Create container image file. Intel devices need a slightly larger file.

if [ $ANDROID_ARCH=armv7 ]; then
cd /usr/local/Android_Images
fallocate -l 1.7G /usr/local/Android_Images/system.raw.expanded.img

else

if [ $ANDROID_ARCH=x86 ]; then
cd /usr/local/Android_Images
fallocate -l 2.2G /usr/local/Android_Images/system.raw.expanded.img

# Format the .img file.

mkfs ext4 -F /usr/local/Android_Images/system.raw.expanded.img 2>/dev/null

# Set SELinux to permissive.

setenforce 0

# Check that the stock Android container exists and is not already a symlink.
# If this is the case, mount it in order to copy files.

if [ ! -L /opt/google/containers/android/system.raw.img ]; then

if [ -e /opt/google/containers/android/system.raw.img ]; then
umount -l /usr/local/Android_Images/Original 2>/dev/null
mount -o loop,rw,sync /opt/google/containers/android/system.raw.img /usr/local/Android_Images/Original 2>/dev/null
else

# If the stock container's missing, check if there is a backup.

if [ -e /opt/google/containers/android/system.raw.img.bk ]; then
umount -l /usr/local/Android_Images/Original 2>/dev/null
mount -o loop,rw,sync /opt/google/containers/android/system.raw.img.bk /usr/local/Android_Images/Original 2>/dev/null
else

# If there's no backup in the expected location, check in ~/Downloads, too.

# NOTE: We can also use a container from a different device/other OS versions by putting it in ~/Downloads.

# To use a different container, we just need to rename any existing containers in /opt/google/containers/android/
# e.g. rename /opt/google/containers/android/system.raw.img.bk to /opt/google/containers/android/system.raw.img.bk.bk
# Containers from different devices/OS versions are unlikely to boot, however.

if [ -e /home/chronos/user/Downloads/system.raw.img ]; then
echo "Mounting /home/chronos/user/Downloads/system.raw.img and copying files"
umount -l /usr/local/Android_Images/Original 2>/dev/null
mount -o loop,rw,sync /home/chronos/user/Downloads/system.raw.img /usr/local/Android_Images/Original 2>/dev/null
else
echo
echo "Error!"
echo "System.raw.img not found"
echo
exit 1
fi

fi

fi

fi

ANDROID_ROOTFS=/usr/local/Android_Images/Original

# Mount the new .img.

mount -o loop,rw,sync /usr/local/Android_Images/system.raw.expanded.img /usr/local/Android_Images/Mounted

# Copy the files.

cp -a -r $ANDROID_ROOTFS/. /usr/local/Android_Images/Mounted

# Rename the original container to .bk.

if [ -e /opt/google/containers/android/system.raw.img ]; then

if [ ! -L /opt/google/containers/android/system.raw.img ]; then
echo "Moving original Android rootfs image to /opt/google/containers/android/system.raw.img.bk"
mv /opt/google/containers/android/system.raw.img /opt/google/containers/android/system.raw.img.bk

# Make the symlink from the original pathname to our writeable rootfs image.

echo "Replacing original Android rootfs image path with symlink to /usr/local/Android_Images/system.raw.expanded.img"
ln -s /usr/local/Android_Images/system.raw.expanded.img /opt/google/containers/android/system.raw.img
fi

else

if [ -e /usr/local/Android_Images/system.raw.expanded.img ]; then
echo "Creating symlink to /usr/local/Android_Images/system.raw.expanded.img at original Android rootfs image file path"
ln -s /usr/local/Android_Images/system.raw.expanded.img /opt/google/containers/android/system.raw.img
fi

fi

# Change the envs for writeable mount and debuggable in CrOS's /etc/init.

sed -i 's/export WRITABLE_MOUNT=0/export WRITABLE_MOUNT=1/g' /etc/init/arc-setup-env 2>/dev/null
sed -i 's/export ANDROID_DEBUGGABLE=0/export ANDROID_DEBUGGABLE=1/g' /etc/init/arc-setup-env 2>/dev/null

The rooting script is basically just the above, with the addition of a couple of other bits, including the relevant commands from the update-binary script in the SuperSU zip, slightly rearranged from Edify to regular shell script for the CrOS shell. That part of the script can be seen here.

So you could maybe do a similar script, with the files you want to flash. Also, once you have a R/W Android rootfs, it may be possible to update files from directly within Android, although, as mentioned in the last few posts in this thread, on some recent CrOS builds, some people have been running into an issue with the rootfs still getting mounted RO within Android, even with a writable container. This does not occur on all devices though, and should be just a temporary issue.

It would probably also be possible to set up a sort of overlay configuration, somewhat similar to Magisk in effect, but due to the somewhat convoluted mount configuration of the container based system, and the almost constant changes/updates (to the container, its config, and so on) that have been occurring with each update to Chrome OS, this would likely require quite a bit of work to implement and maintain.