I am a nearly retired EE 8) myself. Welcome to the forum.
If you can get your program down into a .hex file, it can be loaded. I have a standalone programmer (see below) that will allow you to load a hex file from SD card, or you can take a shot at using avrdude commands to do it.
The Atmel data sheets have many example of assembly code.
Not all shields have code associated with them. You'd have to examine the ones that do on a case by basis to determine if their source code would be Forth translatable.
Forth has come up as a programming option before, if you search the forum you should be able to find some topics.
http://www.crossroadsfencing.com/BobuinoRev17/
