I looked up how to change the player’s default animations and I found that if you copy Roblox’s animation script from the player’s character, replace the ID’s with your own, and replace Roblox’s animation script for this new one when a new player joins, it does exactly this. I have done this and it does work, however, my new walk and run animations are not as smooth as they were when I had them looped in Roblox’s animator plug in.
(If you look specifically at my character’s feet you can see the animation studder, this is not the video quality)
My walk speed is 10 and my run speed is 20.