Changing Boundary Type from Internal to External

How to change boundary type from internal to external?

1) Change boundary into a wall => this will create a coupled wall (wall/wall-shadow)
2) Type the following TUI command : mesh/modify-zones/slit-face-zone => this will uncouple the walls
3) Choose appropriate external boundary for each wall

External boundaries: pressure inlet / outlet, velocity inlet, outflow, mass-flow inlet, pressure far field, wall, symmetry, axis, periodic, inlet /outlet vent, intake / exhaust fan
Internal boundaries: fan, interior, porous jump, radiator and wall