How to change a player's animation live in a server script?

I am making an FE avatar editor. Right now I want to change player R15 animations for other animation packs Roblox released. As of right now, I couldn't get my script working. Could anyone script it for me? Thanks in advanced.

Script I tried using:

local NewClimbAnim = script.ClimbAnim:Clone()
animationScript.climb.ClimbAnim:Destroy()
script.NewClimbAnim.Parent = animationScript.climb

I have also tried cloning the player's animation script then adding the modfiied changes then deleting the player's animation and putting the changed one in the player.