i'd be interested to know if someone can reproduce this
i changed ReplayGain info for all my tracks, then clicked the 'refresh' button on the 'search tool' tab expecting that the new metadata would be loaded, but it wasn't (i could tell by listening) - i had to remove and re-import the library to get the new metadata loaded
audacious 4.2 (arch repo)
The refresh button on the Search Tool just scans for new tracks added. If you switch to the Library playlist and press F5 (or Playlist -> Refresh from the menu) it will do a full metadata refresh.