Save a layout to your library so you can reuse it for future events without rebuilding it.
In the editor, choose Save to library.
Name the seat map and confirm.
It now appears in your seat-maps library, ready to attach to other events.
Working on a map that came from your library? You can either update the original - every future attachment gets the new layout - or save your changes as a new map and leave the original untouched.
Either way, events already using the map keep their own copy, so nothing changes for them until you choose to roll an update out.