Chances are not all your tags will be 100% accurate or show exactly the video that you want to include in the event. Keywords and timings can be modified.

Your questions answered

Can I edit multiple events at once?

Yes, multiple events are selected in the usual ways (ctrl+click, shift+click, ctrl+A). Editing any one of the selected events edits them all.

But what about editing the position and duration of multiple events?

Yes but to change position you would add an offset. For example, editing the position of an event with +5 will add 5 seconds to all selected events.