Depends on the forceI might be missing the point you are making.
Not all repairs or mods are in house for all forces.
Essex do everything
so do Gloucestershire and the MET
but some places where they have a smaller fleet will order them all fitted with graphics, and have a team in to fit the comms, In Southern Ireland they contract it to a specialist company, most forces try to keep it in house, to keep costs down, time, and to stop interference with equipment