RE: I’d like to know how re-importing works. Is it possible?
Yes, it is.
RE: How does the overwrite work? Does the import check for existing or modified info?
If you have a CSV file, hand-crafted or supplied from a third-party source, all rows will be imported as a new directory entry each time you import. There is no duplication-checking/verification.
Can you overwrite an existing directory entry from a hand-crafted or supplied from a third-party source? Yes. If the directory entry already exists in Connection, you can add an Entry ID column to the CSV file and enter the ID that the WordPress database assigned the directory entry when it was added. When importing, Connections will check for an existing Entry ID and overwrite it if it exists.
You can also use the Connections CSV Export All tool to export and edit the file. As the CSV file exported from Connections will already contain the Entry ID column and the correct ID for the entry, when the CSV file is reimported, it will overwrite the existing directory entries.
To bulk import directory entries, you will need the CSV Import add-on. Here’s the link:
I hope this helps! please let me know.