How do I mark translation strings as non-customized?
Based on 4k4's suggestion, I was able to do this with SQL:

drush sqlq &lt; "UPDATE mydb.locales_target SET customized = 0 WHERE customized = 1;"


Warning: This will unset the customized flag for all strings on your site, but leave the customized translations in place.  This is what I wanted, but make sure it's what you want too before running the command.  Always make a backup, etc.