Can do it the lazy way like I do!
Make a loottable with just that specific lootdrop and add it through perl
(they will have their normal drops + the custom stuff from this table)
global_npc.pl
Code:
sub EVENT_SPAWN {
if ($mlevel >=1 && $mlevel <= 20) {
$npc->AddLootTable(104967); #whatever loottable you wanna add to them
}
}