well, I've used a "drop weapon" spell - but I dunno of any "take weapon" command.
you tell me, m8 (when the rep's comes flooding in)
UnitName Action ["Drop Weapon",unit,0,0,"weapon"]
Back in the old days, some of us used to use these spells to simulate the action :
Tomb Action ["REARM", NameOfCrate]; Tomb AddMagazine "m16"; Tomb AddWeapon "M16"; etc.