MM offers a great feature for copying entries from one event (the Source) to another event (the Target). From the Source event, you can copy all entries or any selected set of entries. Just click on the Copy icon from the Seeding Menu to start the process.
There are two methods:
Copy the selected entries to the target event and Delete the entries from the source event
Copy the selected entries to the target event without deleting the entries from the source event.
Note that if both the source and target event match as far as gender, distance and event type, the entry marks will also be copied. Otherwise, just the entries with no entry marks will be copied.