[help] How can I build the Kindle firmware source code?

Hello! New to this Kindle jailbreak scene, as my friend got me a Kindle PW 5 for Christmas. I was wondering if it is possible to modify the firmware source files, then dump them onto the Kindle somehow? I received my Kindle with firmware 5.15.1 :(, and when trying to downgrade, the "Update Kindle" button is grayed out. I had an idea, what if I could modify one of the shell scripts that run when search commands are executed. Say, ";dm" ("/usr/bin/dm.sh"), could I modify this in the source, compile it, then load it onto my Kindle. The optimal modification would be to append this line to the bottom of the script (or wherever applicable):

echo "shell script inject success" > /mnt/us/documents/injected.txt

If it is possible to implement this functionality, can someone guide me to the place, and can somebody help me compile the source

Thanks, blue