This is a challenge, because moving the existing junction box might be tricky. Anytime you have an electrical connection made, it needs to be housed in an accessible box, as per code. For example, if the fixture over the dining room table is 12 to 18 inches off center because of the wall unit, a cover plate would need to be installed over the old junction box when the wiring is extended to the new fixture location. This is not very attractive. In order to avoid this, an electrician would need to pull new wiring that is long enough to go from the existing switch or dimmer to the new fixture location. If the ceiling joists are going in the right way, it is pretty easy to pull new wiring with a minimum of fuss. If the joists are going in the wrong direction, the electricians can use a technique where they cut a ¾-inch-wide slot in the sheetrock and loop the Romex under the joists. They cover the slot with a narrow metal plate, which is then plastered over, meeting code. Here’s another, less-involved option. Depending how far off the new fixture location is from center, you could cover the old junction box with a large-enough plaster medallion or rosette (as in this photo). As long as the medallion is screwed in and not glued to the ceiling, it acts as overscaled junction box cover. These medallions come in all sizes and styles. An oval one might just be the ticket.