To merge (add) or "unmerge" (mass-delete) records from other databases, use the Tools > Merge/Unmerge command. The displayed dialog box enables you to specify how adding or removing records should be carried out:

Options 1. - 3. perform field name matching in the current and the merged tables. You can bypass this using this command in the form of a scripts - please see: ...

Options 4. causes deleting records from the current tables where the specified field values match.

Note: to perform mass-merging tables from a given folder or multiple folders, use a script as shown in the "Merging" scripting examples further in this manual.