Hi,
Is it possible to modify the existing firmware on a programmable XBee S2C?
If so, how should this be done?
Yes it can be done. You need to make sure that the default bootloader application is installed to do it. You can then use XCTU and the Enable this is a programmable module function. Or you can use the remote Firmware update function of the XBee Zigbee firmware via another XBee in API mode.