Quesiton: Can I send my USPro White tile to my National Meteorology Laboratory and have it calibrated, then enter the calibrated values into the firmware for the instrument to use?
The everwhite tile that is supplied with the USPro is calibrated relative to PTFE that was measured on a USPro. This is how ASTM specifies that the Top of Scale be assigned. As a proficiency check we measure a white tile and compare the reading to how NIST read that tile. If there is no difference within the uncertainties of both measurements then there is no difference between the assignments.
I would suggest that your customer do the same. They can either send their tile, or purchase a new tile and send it to NIST/NPL. then when the tile is returned they can standarize the sensor with our tile then read the NIST/NPL assigned tile and compare results. They can do with for both RSIN and RSEX.