How to constantly Raycast (V2)

Well if you want something to do something continuously once triggered then you have a couple options:

You can perform it inside a coroutine:

 private IEnumerator DoThingContinuously()
 {
     while (true)
     {
         // perform logic you want to be carried out each frame
         yield return null;
     }
 }

Bare in mind you have to start coroutines with:

  var myCoroutine = StartCoroutine(DoThingContinuously());

Here I'm storing a reference to it so I can call StopCoroutine on it when I want it to finish.

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Alternatively you can create and destroy new components that perform the action you need:

 public class DoThingContinuously : MonoBehaviour
 {
     private void Update()
     {
         // perform logic you want to be carried out each frame
     }
 }
 
 // then, within the class you're controlling the behaviour from, you can add this component at runtime
 
 private DoThingContinuously instance;
 
 private void StartRunningThing()
 {
     instance = gameObject.AddComponent<DoThingContinuously>();
 }
 
 private void StopRunningThing()
 {
     Destroy(instance);
 }

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For your second point: yeah the direction of a raycast can happily be a Vector3.

 Ray ray = new Ray(transform.position, grapplePosition - transform.position);

The ray constructor takes a direction argument, so if you want it to point towards the grapple point then find the direction as grapple target position minus player position.

Let me know if I've misunderstood this bit!

Lastly, if you're thinking of getting a grapple wire to wrap around objects then I'd strongly advise having this done automatically rather than with raycasts or physics. For example, each grapple-able object having a GrappleBehaviour component that stores points either side of it for the grapple wire to target and handle how the wire wraps around it. If you try go down the route of performing more and more raycasts to find a wire's direction then it'll become very complicated and hurt your frame rate. A raycast to find out what you're hitting is great but additional raycasts to handle wrapping scares me. I might have misunderstood this bit so ignore if I have!