For longhaul flights, the First cabin used to be stripped out and a double bed installed along with a dressing table for Liz and a small dining table. Two (occasionally more) F-seats remained in-situ.
As I understand it, this practice has all but ended. Now the aircraft flies in usual config but with one or two minor changes to emergency equipment and soft furnishings.
That said, I've never been on a royal flight for a variety of reasons, though I hope to at some point.