It's certainly possible. Tracing the MCUs IO lines to LEDs/buttons/relays etc on a PCB is usually pretty straightforward.
I have just finished doing this and writing replacement firmware for the Aqara E1 series of Zigbee switches, after getting fed up with them not supporting basic Zigbee binding functionality.
I have just finished doing this and writing replacement firmware for the Aqara E1 series of Zigbee switches, after getting fed up with them not supporting basic Zigbee binding functionality.