loading a players character to an already exsisting character model?

I have this function, but it wont work, any tips?

I can't use startercharacter because it only changes one players character

function module.test(plr)
	plr:LoadCharacter(workspace["Disease Models"]["Mumps"]["Dummy"])
end

You can add the character model to StarterPlayer and name it StarterCharacter

If only one player would have the character, you can do this:

script.Parent.ClickDetector.MouseClick:Connect(function(player)
	player.CanLoadCharacterAppearance = false -- Make sure to do this
	player:LoadCharacter(workspace["Disease Models"]["Mumps"]["Dummy"])
end)

As you said, this script changes the character of the player who clicked the ClickDetector (which is hopefully only one player).