Hi Dan,
Just a small point, but on approach, the FD pitch function is the same regardless of number of pushes, but assuming that this pitch attitude is flown, the first push gives power for about 2000fpm, the second, full go-around thrust.
I agree that 'reconfiguring' is not the term for the IRS update. In practice, not all databases have all stand positions for all airports, so the FMC position is often initialised for the aerodrome reference point (usually the centre of the longest runway). This is 'close enough for jazz'. A more precise position is required for flight, so the FMC is given departure runway, and 'knows' the Lat and Long of the threshold. If departing from an intersection, the distance from the threshold may (should) be input. Then, on TO/GA, the FMC position updates to that geographical point. This is checked by the NHP. Once airborne, the FMC position depends upon VOR, DME, and these days, mostly, multiple GPS, positions.