If I define an array of strings per https://www.arduino.cc/en/pmwiki.php?n=Reference/PROGMEM but do not reference them in the program, will the compiler include them in the downloaded program or will the compiler leave it out?
You can read the flash by address without using the PROGMEM names.
It is possible to load hex files to flash without overwriting a loaded sketch. Not easy... possible.
Why not figure it out for yourself - compile it with and without the array, and see if the size changes...
Regards,
Ray L.