I just implemented a feature that allows changes to the code to be reloaded when you resume without restarting the whole game:
https://github.com/nesbox/TIC-80/pull/840
It only works when you launch with the -code-watch flag, but if you build from master try it out and let me know what you think. In order to use it you will need to write your game so that the state is stored in a global and that it doesn't reinitialize that global if it already has a value when the code loads. It only works for languages that support eval, which right now is just Lua and Fennel.