Alt,
Changing from, say, LNAV to HDG SEL to avoid a cell is neither disconnecting nor over-riding automation, it is simply changing mode, and as such is not a manual intervention.
Manual flight implies direct control input- i.e via the yolk in a Boeing, and that would NOT be a normal input while the A/P was still connected.
If a sudden, time critical intervention was required, disconnect and manual flight would be appropriate.
Last edited by Wizofoz; 29th September 2013 at 17:13.