Suggest methods for testing changes to "pam.d/common-*" files

PAM configuration files are read dynamically. To test, you can authenticate to the appropriate software and view the logs.

It is often wise to understand all the configuration files in question if you are attempting to make expansive configuration changes.

PAM man page

I usually use the pamtester for checking the pam configuration, this way I can check whatever all restrictions are working correctly on all services that have specific config files without using specific clients for each and every service.