interesting question there; i always thought the ICBMs had the coordinates already set internally?
As in, the launch crew on LAUNCHES, they do not plot the target. The ICBM has a set ot sensors, such as accelerometers, that tells it where it is travelling to. You would likely need to program these to hit a specific geolocation, and while i am sure this can be done on-the-fly with relatively modern equipment, isn't that just an additional step that does not need to be there? SO, each specific ICMB already has its one-or-more targets set, and when you want to hit a specific target, you launch that specific ICBM.