Firmware Development Questions

[Nextstagegauges]

I've just started making some minor changes to the firmware, concentrating on superficial stuff like making the builtin logbook actually show the depth and temperature profiles in feet/ferinheit when set that way , and showing the time in an AM/PM format. I've come up with a few questions so far:

1) The changes I'm making are low risk. Eventually I will make a change that causes a crash, and probably a crash displaying the home screen or something. When I eventually accidentally do this, is there a way to continue to load new firmware, or does firmware updates require functional firmware?

2) For the 12 hour format clock I would like to add a setting for this. Is there a general approach for updating configuration settings when a new one is added during a firmware update? Firmware downgrades would need to be supported as well I imagine. I was thinking of alternatively tying it to something like the MM/DD/YYYY date format, but ideally it would have its one setting.

[Nextstagegauges]

Could also use a hint on the gfx engine, specifically around printing text. The TXT_2BYTE thing is something I'm attempting to get an understanding of, since I think it is hosing up my attempts to append text after the t7 surface time string.