Prefab Animator Attributes Not Updating

I call the following code to set animation speeds and animation transition exit times for my object which is an instance of a prefab:

 public const int idleToAttackTransitionID = 21386;
 [SerializeField] private float spawnSpeed;
 [SerializeField] private float attackSpeed;
 [SerializeField] private float cyclesBetweenAttacks;
  void Start()
         {
             myAnimator = GetComponent<Animator>();
             myAnimator.SetFloat("SpawnSpeed", spawnSpeed);
             myAnimator.SetFloat("AttackSpeed", attackSpeed);
     
             var animatorController = myAnimator.runtimeAnimatorController as AnimatorController;
             if (animatorController == null) return;
             foreach (AnimatorStateTransition transition in animatorController.layers.SelectMany(layer => layer.stateMachine.states.SelectMany(state => state.state.transitions)))
             {
                 if (transition.GetInstanceID() == idleToAttackTransitionID)
                 {
                     transition.exitTime = cyclesBetweenAttacks;
                 }
             }
 }

Now, for example, when I go to the inspector to change serialized field spawnSpeed from 1 (which is the default speed as assigned in the object prefab) to 5 and then play the scene, the object will still run at spawn speed 1. However, if I stop the scene and then hit play again without doing or changing anything, the object will run with spawn speed 5 as desired. Then if I change from spawn speed 5 to spawn speed 10 and play the scene, the object will not run at either speed and will again default to spawn speed 1 before I stop and play the scene to get it to run at spawn speed 10. Then every play after this will run at spawn speed 10 until I change it again where it will go back to speed 1 for a single play.

It is worth noting here that any other values I change will update properly on the first play, so it seems to be specific to the animator. It also seems the problem is somehow related to the object prefab vs instance, but I just can't seem to figure it out.

Thanks for any help! (also if you know of a better way to change transition.exitTime at runtime please leave it here! )