I have found that I'm an idiot once again.
You can change the size of nodes in various ways:
set_size(Vector2 (200, 100)) # Change size manually
set_scale (Vector2(1.5, 1.5)) # Make 50% bigger
When using these you can use them anywhere you like.
But if your node is being used in the AnimationPlayer your changes will not be kept when using
func _ready(): because your animationPlayer will just use all your keyframes for the nodes you are using. We will need to use
func _process(delta): or change the size somewhere after the animation is over.