Can you blend between states?
Yes you can by placing your state machine in a tree structure switched on int for example. You can then change the weight as to how the blend should occur.
Can you dynamically change the animation BP?
Yes you can you can but you will need to reset the local vars. This is usually set with the “Event Blueprint Begin Play” which is preformed once when the animation BP is first ran as to requirements for that BP that does not need to cycle through.
To reset each time you switch the animation BP you need to preform a “Event Blueprint Initialize Animation” so that the “Set” vars are set up.
If you plan on dynamically switching animation though it’s best to do your state change requirements with in the controller rather 6han with in the animation BP as to what BP is required.