A method and apparatus for replacing a defective downhole well safety valve of the full bore type by a wireline valve sealably insertable in the bore of the housing for the defective valve by wireline and operating the wireline inserted safety valve by fluid pressure supplied through an existing control fluid passage provided in the original safety valve housing. An internally projecting integral protuberance is provided in the bore of the original safety valve housing and a connecting fluid conduit is provided between the interior of the protuberance and the existing control fluid passage. A cutting tool is mounted on an axially shiftable sleeve disposed immediately above the protuberance. The axially shiftable sleeve is manipulated by an auxiliary tool temporarily inserted in the bore of the original valve housing and causing the cutting tool to remove the protuberance and thus establish fluid communication for the control fluid with the internal bore of the original safety valve housing. The insertion of a conventional in-tubing safety valve apparatus will permit such apparatus to be operated by control fluid pressure supplied through the opening provided by the severed or removed protuberance.