how easy it is depends on the ragdolls like in normal human like one, you can spawn them like a prop in the pac3 menu and tik on bone merge, and then you just need to make the original character invisible, if that doesn't work you need a lot of events, and that's a longer and more complicated thing to do, if you need any help I would love to help further, but my abilities are limited

If you are talking about a ragdoll that isn't humanoid. (E.G: madness combat characters)
you will need to use the custom animation option. If you talk about Models that are human,just bonemerge them.