I don't fly a boeing, but E170/E190's.
The posters question seems pretty reasonable. We have TO-1, TO-2 and TO-3, all of which we can flex.
Most of the guys in work are surprised to learn that if we use TO-3 with a flex, it does not matter how hard or how far we push the thrust levers, we are not going to get any more thrust than TO-3 no flex, with 2 exceptions.
1. Windshear will give WSHR thrust.
2. Engine failure will give us Reserve power, but only TO-3 reserve.
If we have completley messed up our performance, and the end of the runway, or an obstacle is rapidly approaching and we wan't to get away from TO-3 flex to TO-1, then some very quick FMS programming would be required.
14-06-30 page 4 you can get TO-3 RSV by pushing to max. You cannot change the TO DATASET as the page is removed once the TO is commenced. Windshear will give GA RSV which is equal to TO-1 RSV on most engines.
Sorry for the thread creep.