this could be done with some forced keypresses (which we don't have yet) in 1.19 we will have forceplayer=x or something, wait just read 1.19 beta is out I'll crank out a script right here:
for this, set a knife to the first slot in the editor and make sure to have one, also only have 2 other weapons for this specific script.
place in a trigger zone
:scancodekey=3:varequal=weapnum 2
:scancodekey=4:varequal=weapnum 3
:state=0:dimvar=weapnum
:state=0:setvar=weapnum 2
:state=0:state=1
:state=1,varequal=weapnum 2:weapontoslot=2
:state=1,varequal=weapnum 3:weapontoslot=3
:state=1,scancodekey=47,currentweapon=2:setvar=weapnum 2,state=5
:state=1,scancodekey=47,currentweapon=3:setvar=weapnum 3,state=5
:state=5:weapontoslot=1,plraction=9,state=1
now this will work IF the command "weapontoslot" means "switch to this weapon" if not, we have to wait yet longer... And etimers might be needed to pace this
I appear to have burst into flames...