It is possible to modify wall properties or wall type individually or for selections of walls.
You can change from a single wall to a compound wall, it can be better to change to Compound Walls later in the design process where possible, working with single walls is more straightforward in the early stages. Changing the wall width is easy, junctions all connect simply, clean up is minimal.
Once you go to the compound wall junction connections may not be as straightforward, some manual clean up may be needed. Refer to help on compound walls for guidance on setting priorities for the various layers.