The purpose of creating a wall by face is to ensure the design concept, which was created by the mass element keeps it relationship with the wall. If the mass changes the wall can be updated to ensure seamless work flow.
if you need to edit independently you'll need to break the relationship. Really depend what you are trying to achieve, the LOD and LOI for the model and your workflow.
I assume you created a concept mass to created the wall due to the shape, angle or form. is there a reason you don't want to edit the mass to get the new form, shape, angle you require?
Walls created by face that are adjoining will clean up, if you edit the wall by face to extend or trim then no clean up will occur.
Hope this helps
