Create a vertex in a specific point of a plane

I have a plane and I want that when a sphere touches a certain place in the plane, for that place (vertex) to move to a certain location in order to deform the plane.
I know the code to deform the plane by accessing its vertexes (code I list bellow), but I need to create a new vertex in a specific position. Is this possible? How?

My thanks in Advanced

Code (csharp):

1.  
2. Mesh mesh = new Mesh ();
3. mesh.Clear ();
4. mesh = mainObject.GetComponent<MeshFilter> ().mesh;
5. Vector3[] vertices=mesh.vertices ;
6. float fl = 0.2f;
7. vertices[41]=new  Vector3(vertices[41].x+fl, vertices[41].y, vertices[41].z);
8. mesh.vertices=vertices;
9. mesh.RecalculateNormals();
10.  

 

I'm trying something like the code I post bellow in order to select the vertex, but after using linq I'm not able to determine the index position of the selected vertex (this is, if the code really works besides that, because I don't know if it's doable)

Code (csharp):

1.  
2.         Mesh mesh = new Mesh ();
3.        
4.         Debug.Log ("MESHTEST Ceph Point");
5.        
6.         mesh.Clear ();
7.        
8.         mesh = mainObject.GetComponent<MeshFilter> ().mesh;
9.        
10.         Vector3[] vertices=mesh.vertices ;
11.        
12.         var V3=(from cur in vertices
13.                where (cur.x==ponto.PontoX) && (cur.y==ponto.PontoY)
14.                select cur).FirstOrDefault();
15.