"Swap" NPCs on an object

I wish to know if it is possible to "change" an NPC on a door.
Here's the deal: I want to have a shop NPC during the day, but during the night change it with a non-shop NPC.
My theory is: Script the object that once used, check the time, if it is during the night, make the player talk to another npc instead of going to the store that will be closed at night, if not "default".
In theory is easy put everytime i tried, the spaghetti code that i wrote made the Editor explode.
Help?

Set the shopkeeper as the default NPC for the door then put this code on the door:

if(evtuse())
{
if(isNight())
talknpc("NPC id here");
else
default();
}

Set the shopkeeper as the default NPC for the door then put this code on the door:

if(evtuse())
{
if(isNight())
talknpc("NPC id here");
else
default();
}

Thank you