Then if the product becomes a sell-able thing, the hardware shifts to a more permanent solution of dedicated PCB's and chips, etc?
"Is there a way to upload once and then freeze the board from any further up/downloading of the content?"What makes you think your code cannot be duplicated by another software person?.
However, I'd rather someone do their own version from scratch, than use mine as a starting point, then change the bits they don't like.
Incidentally that is also how evolution works
Obligatory "Other belief-systems are available.".