Will Laying Additional Sockets Spoilt The Cornices/l-box

Just bought resale flat, would like to keep the L-box ****/dining and cornices inside rooms. If I add in additional sockets in the room (for example additional 2 sockets in mbr and two more in another rooms), will the existing L-box/cornices be spoilt? Cos I think the electrician needs to remove the cornices in the room and L-box in the dining hall in order to lay the cable from the room to the DB right?

Thanks