However if you want to change that start screen it's as easy as writing a new image file called '.splash' - no text is displayed on top but you could hard-code the MAC address in there.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
You're probably looking at somewhere like this: https://github.com/espruino/Espruino/blob/c09de7bc3a206760f16fd9482c2152dd73a9f605/libs/banglejs/jswrap_bangle.c#L3042
However if you want to change that start screen it's as easy as writing a new image file called '.splash' - no text is displayed on top but you could hard-code the MAC address in there.