2016 maxima. Is it safe to unhook the negative from the battery and let it sit for however long to reset the computer. Going back to 91 octane. Well 93 really. Car ran fine but just scared I'm missing something or getting worse MPG but no way to test it.

 

Going back to 91 octane from what? If you switched to regular just switch back. You don't need to reset anything. The car will adjust.

 

Totally safe and won't hurt anything. Disconnect for like ~10 minutes. You will need to re-adjust your radio settings, e.g. Bass, Treble, etc but that's it.