I am playing with DarkPlaces engine.
I have accidentally pressed F10 instead of F9 a few times, and it tires me that it quits the game. It's also redundant as the same can be done through Alt+F4.
I tried modifing config.cfg in id1, deleting the line (bind F10 "quit") but with no result. Any ideas apart from receiving electrical charges every time I press F10 until I learn not to do it?

As you say there already is that line in the config, maybe your change wasn't saved properly or it wasn't the right config file. While you're in the game, try to type "bind F10" in the console (opened by pressing ~ or ^ on your keyboard) to see what the game itself says the key is bound to. If it's still "quit", try to change it to something else in the console directly.

I don't know about Darkplaces, that function could also be hardcoded, but I highly doubt it. If all else fails, classical conditioning should still be a very effective option!

It's been a long time since I used DarkPlaces, but
unbind f10
should work in the console.