Ah okay, I see your concern. Are you using the Pi version or not? If your using the Pi version you could just have a script that restores a default config every night like you suggested.
If not, I don’t think you can currently do what your wanting. You either depend on the server or don’t. However, instead of doing a 0% (if your trying to prevent a program running) you can do a rain delay. That has a timer by default. Of course limited but again not sure how aggressively you want to modify your watering.
Of course, you can also modify the actual firmware on the OpenSprinkler to use weather control directly. I know with version 2.0 it has a lot more memory and could possibly accommodate something like that.