How can I change core animations during the game?

In my game, players are able to go into an animalistic mode where they go into all fours, I achieve this by changing the core animation IDs to a custom one. However, the animations only change if that specific animation stops, for example, if the player is running and then activates this mode, the default animation will continue until the player stops moving which stops it, and then the new animation takes over and vice versa with the idle animation.

My current solution: i change the animation IDs and disable then re-enable the core animation script. It's rudimentary and I have to do this twice within 3 seconds as only doing it once blends the new animation with the core animation (ROBLOX glitch?).

How do I change animations the moment they are activated? Rather than having the player stop the animation that needs changing. Other games achieve this smoothly with crouch animations.