I noticed that when i ran link_bibs_to_authorites.pl with --test, it calls LinkBibHeadingsToAuthorities in Biblio.pm, which if you have the AutoAddAuthorities syspref enabled, calls AddAuthority, which results in auth_header being inserted/updated. So the --test option won't prevent updates. This can burn someone if run in production. It correctly skips ModBiblio in the link_bibs_to_authorites.pl script. I was doing a test run migration from 3.0 to pre-3.10 master(2012-10-10) and had deleted all my auth_header records. Of course after rebuilding my biblio/auth zebra index (-b -a -r) I ran the script with --test, but saw auth_header records were added. Since my library only had machine generated auth records, and I needed to clean up duplicate authority records from 3.0 behaviors, I was taking this route since no deduplication script exists, yet.