I need to lower a power socket by about a couple of feet. It was original sited over a worktop in a kitchen, but the house has been revamped so that this is now in a living area and I'd like to lower it to be in keeping with other living areas. What is the best way of attaching the extra length of cable required so that the join can be plastered over? Or do I need to strip it back and replace the whole section which is buried under the plaster?