737 - If you're at 3000' and capture the g/s, there is nothing to stop you setting g/a of 2000'. It won't capture at 2000', as you are in app mode.
For an NPA we now set MDA in the alt window, and once more than 300' below g/a alt reset that into the window.
In all cases the 1000' point is the reminder to check it is set.