Aaah i completely misunderstood your reply i thought
you were talking about obstacles you could add and remove for avoidance....

Yes you do not need to use the detailed meshes you can use low detailed models
For the objects that get fed into the navmesh aslong as carves out an area bigger than the object ...thats why also i thought about
the editor because by creating the mesh to be fed into navmeshing instead of all the
geometry you are speeding things up you can control detail to a better degree and make sure
you have the mesh in areas you want pathfinding ,it takes away alot of triangles that arent needed
for filtering so yes its possible and basicly you could create the whole walkable area mesh
inside of a modeling application aswell ..