Our national competition rules are translation of Sporting Code 3 Annex A, and I've done the translation myself. Some paragraphs were omitted because they were needed in international events only, and some were slightly modified. Since we do not have IGC class structure, that paragraph was rewritten completely. The job took few evenings and 99% of the effort was translation. We update rules every year after Annex A update (usually a line or two). Contest organisers provide local prodecures suited to their needs. This has been going on for at least a decade without any problems.