I attempted to make the player who steps on the script's Parent (a Part in workspace) go into the HumanoidStateType.Ragdoll. Here's the script:

script.Parent.Touched:Connect(function(part)
	local parent = part.Parent 
	local human = parent:FindFirstChild("Humanoid") 
	if human then 
		human:ChangeState(Enum.HumanoidStateType.Ragdoll)
	end
end)

The script doesn't work, even when using a repeat wait()... until method

Solution

You can only change states with a local script. If you want to force a state, you'll need to keep changing it.

game:GetService('RunService').RenderStepped:Connect(function()
	Humanoid:ChangeState('Swimming')
end)

Ragdoll Resources

I've recently used Tom_atoes Ragdoll script, it works great especially if you know how it works: https://devforum.roblox.com/t/tom-atoes-customisable-ragdoll/259927

This property released a while back. Many developers in the comments posted their code for it, you can use it: https://devforum.roblox.com/t/humanoid-breakjointsondeath/252053

Humanoid.Sit = true