A simple conversion really. Just don't be alarmed if the colour if the wires are not as expected. Its even more ineresting when all the wires are black...
As in the current release of the 121 by Hornby, even though it is DCC ready, but not for lighting, the board provided does at least have soldering points when you work out which relates the relevant colour wire
and yes it is possible to wire it up so thatyou can use male/female plugs incase you have to remove the body if youve fitted compartment lighting.