I've successfully uploaded the firmware three times now so I know, with persistence, it is possible. I quite like tinkering with the coding. I've just added an extra instruction to the start-up script so some filament is extruded before it starts printing properly. I've been finding, on my cheapo printer, that it takes quite a while before the filament flows which, until now, I've overcome by printing a large brim. Now I've started using hairspray on the bed I don't really need a brim so I want the extruder to be primed before it starts printing.