I need a rigibody to move through an object but the object needs to react to the rigidbody

I am building an excavator sim/game and I got to the point where I am using rigidbodies to control the arm and bucket. The ground is a mesh (I cannot use Terrain) and I got it to react when the bucket hits it.

The mesh reacts by lowering the vertices where the bucket hits. Ofcourse I want to be able to dig a deeper hole so the script recalculates the meshcollider to keep track of the new hits. To keep the frame rate up I use a Coroutine for this. To make the game faster I want to recalculate every half second or maybe even every second, the bucket is not moving at a very high speed so the ground doesn't need to be recalculated every frame, there will be enough mesh to hit to get a good looking hole.

That all works fine, the problem is: when the recalulation is done the bucket bounces off the new collider. How can I make the rigidbody of the bucket ignore the meshcollider but let the mesh and meshcollider react to the bucket?

     void OnCollisionStay(Collision collision)
     {
         if (collision.gameObject == Bucket)
         {
             foreach (var contact in collision.contacts)
             {
                 Vector3 Direct = contact.normal;
                 if (Direct.x < 0) { Direct.x = 0 - Direct.x; } //set values positive if negative for comparison
                 if (Direct.y < 0) { Direct.y = 0 - Direct.y; }
                 if (Direct.z < 0) { Direct.z = 0 - Direct.z; }
 
                 if (Direct.x > Direct.y) { AddDepression(contact.point, 1, -Vector3.up); } //if ground is more than 45deg. vertical just move down
                 else if (Direct.z > Direct.y) { AddDepression(contact.point, 1, -Vector3.up); }
                 else { AddDepression(contact.point, collisionRadius, contact.normal); } //else move down in proper direction
             }
         }
     }
 
     public void AddDepression(Vector3 depressionPoint, float radius, Vector3 direction)
     {
         //recalculating where it hits when plane is not on 0,0,0 coordinates
         float ImpactPointX = depressionPoint.x - plane.transform.position.x;
         float ImpactPointY = depressionPoint.y - plane.transform.position.y;
         float ImpactPointZ = depressionPoint.z - plane.transform.position.z;
 
         var LocalPos = new Vector3(ImpactPointX, ImpactPointY, ImpactPointZ);
 
         //in Start() the vertices of plane are put into a List called modifiedVertices
         for (int i = 0; i < modifiedVertices.Count; ++i)
         {
             //is the vertex whithin a specified distance of the contact.point
             var distance = (LocalPos - modifiedVertices[i]).magnitude;
             if (distance < radius)//yes it is!
             {
                 var newVert = modifiedVertices[i]; //get coords from existing location
                 newVert = newVert + direction * maximumDepression; //move from existing location in the direction of contact.normal * a maxdepression
                 modifiedVertices.RemoveAt(i); //empty old coords
                 modifiedVertices.Insert(i, newVert); //write in new coords
             }
 
         }
         plane.GetComponent<MeshFilter>().mesh.SetVertices(modifiedVertices); //set new vertix locations
 
         StartCoroutine("RecalculateMeshCollider");//calculate new collider, needed to dig further
     }
 
     IEnumerator RecalculateMeshCollider() {
         Physics.IgnoreCollision(plane.GetComponent<Collider>(), Bucket.GetComponent<Collider>());//switch off collisions for smooth movement through ground
 
         plane.GetComponent<MeshCollider>().sharedMesh = plane.GetComponent<MeshFilter>().mesh; //set sharedmesh to new mesh
         yield return new WaitForSeconds(1); //wait a second
         Physics.IgnoreCollision(plane.GetComponent<Collider>(), Bucket.GetComponent<Collider>(), false);//switch collisions back on (and launch bucket apparently)
     }