A room can be mirrored or flipped at any time. To flip the project space, go to menu Room | Wall and press flip room vertically or flip room horizontally.
Take note when flipping the room, the placed objects keep their original order number. Most sanitary objects are symmetrical and can be flipped without problems. But pay attention to shower wands etc.
Set the preference to (dis)enable that products are mirrored while flipping a room. Go to File > Preferences > Defaults > Sanitary.
In the Parts lists mirrored sanitary objects are coloured red, so you can take note.