I would bet there is a better solution than this, but here is an idea. Come at it from the other direction. Replace the data source file with a new one with the new data and give it the same file name. Then you don't have to change the Publisher set up.
I still use an older database program for mail merge with Publisher, and I have always just changed the database file instead of the data source. I originally created a database with the data I wanted to merge and named it 'mailfile.***' and chose it as the data source when setting up the mail merge in Publisher. Now when I want to use a different merge data I just create a new database file with the new merge data and save that database as 'mailfile.***', overwriting or renaming or deleting the old file. When I open Publisher it automatically merges the new data as it is still looking at the same file name. No need to make changes in Publisher.
DavidF