Enlarging a window/doorway in a wall

If I want to enlarge a window, or small opening in one of the walls in my apartment above a neighbour’s apartment, into the size of a door, then fit a door, is it necessary to have OC permission to do this?

Does it matter if the wall is load-bearing?

As such work would require a lintel to support brickwork above the doorway, might this require council approval and therefore a DA, or might it fit into the Exempt and Complying Development Codes, so that no approval would be required?

In that case, would at least an engineer’s certificate be needed to present to the OC?

Petard