Real pivot rotation of all vertices in a mesh?

I need to rotate a mesh by actually moving all the vertices, NOT by changing the transform.rotation of the gameobject. In other words, the mesh should rotate by the vertices, but the tranform.rotation of the mesh remains unchanged at 0,0,0. So, say I have a vertex located at x,y,z of 50,0,50... how would I rotate that vertex by 60 degrees clockwise around the y axis? Assuming the pivot point of the mesh is centered at 0,0,0?