Often during the design of a project the type of Wall will change. If you are using Composites this could mean an change from a 90mm timber frame to a 20 series masonry block. Simply changing the Wall from one type to the other will result in the (typically) interior space getting smaller. The alternative
You can join sections of paralell wall together using the Merge Walls command. Select your pieces of paralell wall, go to Design>Complex Profiles>Merge Walls. The wall sections don’t even have to be touching.
When placing exterior walls always have your Reference Line on the outside. This consistency means that if you globally change your exterior material it will be correct.