The Boeing 737 maintenance manual only refers to fitting and removing the crew seats.
If you want to change a harness a very common task you have to certify in accordance with the CMM.
A number of aircraft manufacturers refer you from the maintenance manual to the CMM.
You can sign i.a.w the CMM providing you can comply with any special provisions e.g special tooling, NDT, testing e.t.c.
Overhauling an item as opposed to repairing it is a whole different ball game.