When attempting to import after changing the duplicate matching rule the import fails. The import will appear to succeed, but no tags will be created or assigned and only one or two records will be created out of anywhere from 2 to 200 or more (I haven't tested with more).
The following is an e-mail I wrote regarding this bug:
I finally was able to reproduce the error I was seeing when importing
(see mailing subject: "Problem Importing with CiviCRM 1.7 Beta 9019"
**) in the Demo site AND on my own site. I upgraded to the latest
Beta version of Civicrm: 9101 and am using Drupal 5.1 along with PHP
5.1 and MySQL 5.0.
Here's how I reproduced it:
Administer CiviCrm -> Duplicate Matching -> Edit Rule (there's only
> First Name change to " Contact Fields -" (which I'm
hoping disables checking of the first name)
> Last Name change to "
Contact Fields -" (same) -> Save
Then proceed with the import as described in the e-mail (