Regarding your question on replanning: On the fly we won't generally have time to completely redo the procedure, and there's a lot of overhead to setup an EVA,

Regarding your question on replanning: On the fly we won't generally have time to completely redo the procedure, and there's a lot of overhead to setup an EVA, so once outside the airlock we'll avoid scrapping the plan entirely and coming back inside unless there's no way to accomplish anything useful. We almost always have extra tasks, which we don't consider part of the nominal procedure. These tasks can be used if for some reason we couldn't do part of the nominal procedure, or if we get the nominal procedure done vastly ahead of schedule and want to use the EVA time we already had book kept. If, say, EV1 is 30 minutes ahead of EV2 and would otherwise just be waiting for EV2, we could send EV1 to do one of these extra tasks. In those cases normally we won't rewrite the procedure in anyway. A voice call will be made to the Flight Director (which everyone in mission control can here) saying something like "After EV1 completes step 45 he will have to wait for EV2 to complete step 56. We estimate that EV1 would be waiting 30 minutes. As such, we suggest he procede to Get-Ahead procedure 'Install Widget' on page 33"