Changing a NPC's HumanoidRootPart's CFrame won't change the NPC's position in local scripts?

This question might sound confusing but i'll try to make it understandable.

So basically, the issue I am having is, when I try to set the CFrame of a NPC's HumanoidRootPart/PrimaryPart with a local script, it doesn't change the NPC's position.

Example:

while wait(.25) do
    script.Parent:FindFirstChild("HumanoidRootPart").CFrame = script.Parent:FindFirstChild("HumanoidRootPart").CFrame *CFrame.new(0, .1, 0)
end

It works perfectly fine in normal scripts but it doesn't work in local scripts.

This isn't really a script problem, more of a question I need answered.