So, I've found a way to disable the Last Man Standing mechanic for all difficulties, by modifing the file "globalsettings.xml" inside of the game's files, going to <LastManStandingSettings> and setting all values to 0. This will make it so that you will die instantly regardless of how many painkillers you have.

I bet you can see where I'm going with this. I never liked the last stand mechanic, but oldschool difficulty is kinda boring since it's too easy. But with this, I can play hardcore diff without last stand, and I'd like to speedrun the game on glitchless hardcore difficulty with last stand disabled.