In that case we can also just update the git checkout too.
One other nicety of a change like this is that it could make the rollout of more extensive changes to searchfox a little easier. Specifically, for the structured analysis branch, especially if we go forward with linking as proposed, we run into the issue of the taskcluster jobs for older branches of searchfox potentially not producing what the trunk indexing jobs want and thereby experiencing some level of breakage/degraded functionality. But if we, in effect, let them be totally isolated, we could specify that the config2-4 should continue to use an older "stable" branch of searchfox for indexing until such time as we're able to make sure we've uplifted changes to the older branches (or the changes just get there naturally) or ensured that the we've dealt with or understood and accepted any fallout/drift. (The structured analysis changes themselves I think are fine, but imply removing the existing in-mozsearch XPIDL indexing.)
Logistically: We could presumably have a deployment helper tool that scans the list of existing web-servers, checks their revisions and how far they are from trunk, then determines whether anything has changed that would mandate a re-indexing or if just updating the checkout is sufficient. I guess changes to anything but
/docs/ would probably want to presume a re-indexing.