The registry in Jomres (stored in /jomres/temp/registry.php) is a record of all files that Jomres can run as discreet scripts.
Originally (in V2 of Jomres) these files would be automatically discovered by Jomres each time it ran, however as time went by we realised that as a system's library of minicomponents grew, this discovery process could potentially slow a system down so we broke the minicomponent's handling down further to the minicomponent registry, and the mcHandler.
The registry is basically the record of where all the runable files exist, whilst the mcHandler actually calls these scripts to be run. As a developer you should never need to manually edit this file. If you want a new minicomponent to be recognised and used by the system you should use the Rebuild Registry button in the administrator area of the CMS. In effect, all this button does is deletes the registry.php file from the /jomres/temp/ directory and forces Jomres to rediscover all runable minicomponents. You only need to use this button once each time you copy a core minicomponent to a subdirectory in the /jomres/remote_plugins folder, or add a new one. You don't need to run it each time you edit these files. The registry is simply a record of these file's locations, not their contents.