Lederhosen is correct. It will be important that the original manufacturer provides the upgrade modification scheme if any. Modifications and/or paperwork, if required, is best done by a manufacturer. Then use an approved organization in order to forestall any future difficulties across national borders. It is not easy to re-register Ultralite aircraft across national borders. There are currently no standards agreed by the EU nor between other states for microlite/ ultralite call them what you will. Each country approves these aircraft types wholly on its own terms. Usually the original manufacturer design standards are acceptable but this cannot be assured.