Just looked at a board in a friends house next door to me . I have same board with only one rcd fitted . His has two fitted but I think the extra one has been added at a later date as rcd looks newer than everything else so his is now dual rcd board and everything is covered by rcd . I know you can buy a blank board and put what you want in to suit but can you “ convert “ a single rcd board to a dual . All looks fine but would manufacturers warranty be invalid or anything like that . Tia