You could add lemon juice to the icing when you get that far, as well as adding it and brandy to the cake. If you make your own icing, I would stir it up with lemon juice instead of water, and use tart jelly under the marcipan, crab apple or rowanberry and apple for preference.
If your cake is still too salt, it will go down in family history, as the year GS helped Grannie make the Christmas cake, and as some Roman soldier, stuck in mud to his knees said to his companion, "Perhaps one day this memory will make us laugh" What he actually said was, "Forsan, olim et haec meninisse juvabit!" in case anyone was wondering.