Starting in the 2019 version, it's even easier to change a room layout by simply splitting a wall in two (or three, or four...) and moving the resulting walls. This lets you quickly and easily change the shape of a room, for example a rectangular or square room can quickly become an "L" shaped room by dividing a wall and moving one of the two newly formed pieces.
Click on the "Split" button in the Layout Ribbon (see the below image)
Select which wall to divide and the exact point where you want to carry out the operation. You can use either the left mouse button to manually indicate the split point or you can enter the exact distance from the newly created edge to those already existing in the layout. With the TAB key, you can switch between right/left distances: the highlighted field is the active one.
It is important to note that if you split a wall that has already been tiled, the application will not keep the existing tiling on both of the newly created walls. It is recommended, therefore, that you first decide the room layout before you begin tiling.
This article is valid for the 2019 version and later.