There is no way to mess with it currently without having sv_cheats set to 1. The minute you turn sv_cheats to 0 it goes back to default.

If you put sv_cheats 0 in your autoexec or your config file, it will automatically have the melee decay turned on, but you will also only be able to have 3 player infected spawned at any one time (someone will get stuck in "entering spawn mode"), and the "cant spawn" radius around the survivors for the infected will grow by about 50%.

With all due respect, the only thing that should be adjusted with survivor melee is that it does less damage at the lower difficulty settings, right like infected melee damage. for the survivors "melee spam" to truly be effective, there has to be more then one of them doing it therefore leading one to believe teamwork was a factor. Its not like it's impossible to break a closet melee spamfest. Boomer goes first, during the explosion the hunters get in the closet while the survivors are knocked back and unable to melee. The problem is the survivors all being crammed in one place makes a hunter or smoker less effective by default, which is fine imo.

To many people have the wrong idea about how vs. mode should go. It's a war of attrition where the infected have to whittle down the survivors medpacks and keep things as crazy for them as possible so they get seperated and thus become easy infected bait. Unless you get the occasional spawn cycle where you have 3 hunters and a smoker and no boomer, it's just not possible to "instagib" the survivors as there is always one guy you can't "control". That's why maps that can be quickly traversed such as stage 1 of blood harvest and no mercy and stage 04 of blood harvest are huge survivor edge maps. (survivors can speed-run from spawn to safehouse in under 2 minutes on blood harvest 04 and actually outrun the director's ability to spawn npc's.)