An admin (e.g. David or Ben) is needed to go to the project on http://projects.kde.org, Settings, Information, and change the location in the combobox.
Search/replace from the old location to the new, in all files.
Adjust kf5-*-include for the new repo location. Usually this means removing special cases :)
The job descriptions on build.kde.org usually have the projects.kde.org full URL in two places, which need to be fixed: description and repository browser further down. Then the project should be rebuilt, in all configurations.
If the repo is already translated, you need to fix scripty. Check out svn+ssh://[email protected]/home/kde/branches/stable/l10n-kde4/scripts and svn+ssh://[email protected]/home/kde/trunk/l10n-kde4/scripts
For instance, when moving a repo from a kde4 module to frameworks, it disappears from kde4. The fix for that particular case is to re-add it by hand in the file get_paths, function list_modules, see the lines about kactivities.
If the repo moves between modules that are both listed in get_paths already, then the .pot will move between subdirs of "templates". This is an issue, since existing .po files get disconnected from the new template (.pot). Two solutions: either cheat in get_path to force the template back to where it was before, or move all .po files to the new location. It all depends on which location "makes sense" for this branch of l10n.