A jig and a method for modifying a casing in a turbine system are disclosed. The jig includes a body and a protrusion extending from the body. The protrusion is configured for engaging a hole defined in a spot face on the casing. The jig further includes at least one machining passage defined in the body, the machining passage provided for machining the casing therethrough, and at least one alignment feature configured on the body, the at least one alignment feature provided for aligning the jig with respect to the casing. The method includes engaging a jig with a hole defined in a spot face on the casing, aligning the jig with respect to the casing, and machining at least one installation hole into the casing through the spot face.