Hello Gentelman,
Next question from me is landing right there and thank you in advance for all your responses. Are you supporting somehow firmware on the air or programmatically updates ? Is is possible to download some kind of hex file via bluetooth, gsm even not wireless but also uart or spi, store it on external flash and update firmware programmatically ?
you want IFU, in-field update. Works over whatever communications mechanism you can get but implementation of the handling of that portion is up to you