why can't the script change the mesh Id of a dummy to the one of a character?

it's impossible to do this:

workspace.Dummy.UpperTorso.MeshId = game.Players.LocalPlayer.Character.UpperTorso.MeshId

SO How can I do that? I don't want to clone it. I just want to make the upper torso's mesh exactly the same as the players.

and if I do it gives an error that the script access is restricted. Is there any way to possibly do this WITHOUT cloning anything.