Release Engineering uses a few unique Bugzilla flags to coordinate changes to the build infrastructure.
Note that only one of these flags should be set - if the patch is low-impact and has been well-tested in staging, then needs-reconfig is appropriate. If the tree should be closed, then do not also set the needs-reconfig flag, as the patch might then be accidentally landed without closing the tree.
If a change requires a reconfig of one or more buildbot masters, then set this flag to ?, but do not land the patch. This indicates that the patch is ready to be landed, and will need a reconfig shortly after landing.
At appropriate times, whoever is on build duty will collect needs-reconfig? bugs that can be landed together, and re-flag them as needs-reconfig+. Once the patch is landed and the appropriate reconfigs done, the flag is removed altogether.
This flag works about the same way as needs-reconfig: set it to ? on bugs that need to be landed while the tree is closed. Part of build duty is to select bugs for landing (setting the flag to +), schedule a tree closure, and land the bugs appropriately.