The crosswond is demonstrated using both the crab and the forward slip techniques.
If the test pilot finds that one technique is unsuitable for the average pilot then the expected technique will be put in the flight manual.
The aircraft undercarriage must be capable of withstanding certain sideloads etc as per FAR-23 or CS-23 as appropriate. This may not be part of the flight test programme if the certifying authority accept an alternative method of demonstrating compliance.
The maximum crosswind demonstrated during test flying of the aircraft is specified in the flight manual. If you choose to use a higher figure then feel free to be a test pilot. However, please check your insurance for the small print about using the aircraft for development testing.
When you have demonstrated the higher crosswind, please let the manufacturer know......they will either amend the flight manual or recomend that you have the aircraft checked due to undercarriage side load limitations.
I wonder which?
Regards,
DFC