Are you looking for something like that: release-script.googlecode.com/svn/Premium disguise headgear.txt (sorry, the tag doesn't seem to properly show the link) ?
If yes, then the part where the look is actually changed is this:
OnPCLoginEvent:
if (hastop) changelook 4,premiumtop;
if (hasmid) changelook 5,premiummid;
if (haslow) changelook 3,premiumlow;
end;
The NPC will let the player select the headgar they would like to see on his or her character and saves the headgear's view id into the premiumtop, premiummid or the premiumlow variable. In addition, the variable hastop, hasmid or haslow will contain 1 if a player has saved a disguise headgar and 0 if he or she hasn't (which I would not suggest, because you could just check whether premiumtop, premiumid or premiumlon is set or not without needing an other variable).Whenever a player logs in, it will then change the look of the player to the earlier saved view id.