I cannot assist with LUA, sorry. However, for those that may be curious to the Perl equivalent.
Code:
sub EVENT_SPAWN
{
@name_list = ("Guard Williams", "Guard Malone", "Guard Baxter"); ## can add as many as you'd like without any further changes to code
quest::npcgender(quest::ChooseRandom(0..1));
$npc->TempName($name_list[quest::ChooseRandom(0..$#name_list)]);
## $npc->SendIllusion(x,x,x,x,x,a); to affect face change a (for Perl, unknown for LUA sorry)
}