I can't be 100% sure as I'm only part-way through my flight mechanics course, but as I understand it the critical wing stalling angle is constant for a given wing profile or cross-sectional shape.
If you extend the flaps then yes, the mean chord angle relative to the oncoming airflow will change. However, the cross-sectional properties will also change (as that's the whole point of flaps) so the stalling angle would also change. I'm not really sure, but that's my tuppence anyway. Oh and I think there's a difference between wing stall and aircraft stall. Talk to me in 6 months time
