Reminders deleted To Do UID

Once a To Do has been deleted in Reminders, it is apparently impossible to re-import that reminder if it has the same UID.

I am syncing To Do items created in, and exported from, FileMaker Pro, into Reminders via an ICS file. If a User has deleted a To Do item, I can no longer sync that To Do item via an import. If the ICS file has a To Do item with a UID that a deleted item used, Reminders simply ignores that item when importing the ICS file.

How can I reset the used UIDs or resurrect a deleted ToDo?