By *"Are you sure duplicating this class is required?"* do you mean that I should leave the original code intact and write a page that would hook into the original code, or do you mean keeping both the ```XWiki.Registration``` and this file?

To the former, my guess would be that it is not required, but would be rather painful.

To the latter, are you sure that it will be possible to merge with all the changes? If merging is high priority, it would make sense to leave the original registration intact, and use the macros from it instead, would it not?