they are already implemented in rAthena, maybe someone could make a pull request here? They are very useful for events hope everyone agrees
/* Work In Progress [Lupus] BUILDIN(addmonsterdrop) { int class_,item_id,chance; class_=script_getnum(st,2); item_id=script_getnum(st,3); chance=script_getnum(st,4); if(class_>1000 && item_id>500 && chance>0) { script_pushint(st,1); } else { script_pushint(st,0); } } BUILDIN(delmonsterdrop) { int class_,item_id; class_=script_getnum(st,2); item_id=script_getnum(st,3); if(class_>1000 && item_id>500) { script_pushint(st,1); } else { script_pushint(st,0); } } */