Is it possible to retrieve the CAS product ID from a program? As far as I know, there is no in built command to do this, and the only way I can find is by using a lua script running the command platform.getDeviceID(). My idea is to somehow integrate a lua script into a TI program, which I'm not to sure if a method exists? If so, the program could call the lua script to change/define a variable with the product ID and display this. Any ideas?

You can theoretically run Lua code by making a Lua interpreter in pure TI-Basic, but it will be impossible to retrieve the Product ID without delving into Assembly language or C or ICE.
If you know some z80 ASM, here is a good place to start. https://wikiti.brandonw.net/index.php?title=83Plus:OS:Certificate/Headers