By default the plugin manager consider two repositories: 1) The official list of plugin. Which is the plugin_repo.list file from this git repository. 2) The local cache directory if used. Thus, plugins that have been cached in previous executions are known by the plugin manager.
User can add repositories, either through the plugin manager GUI, or through GroIMP’s options.
Once added, a repository remain known by GroIMP between different executions. The repository can be activate/deactivate without beeing removed.
After modifications on the repositories (changing url, adding/deleting, or activating/deactivating), they need to be reloaded. This is performed in the GUI by the menu data>Reload repositories. Or by using the command /pluginmanager/commands/data/reloadRepo.