First use of real VCS power - made this change to an old version of the file (gamma 6 build 002, as opposed to the current dev files), committed it to the release branch, updated the download's changeset ID, and merged the changes to the current dev files.
Worked beautifully.
No new stuff leaked, no manually editing a bunch of files, no manually adding files to the download, no unintended changes that cause new errors. So glad we spent a month redesigning that whole process.