For the purpose of initial certification control (measurement), is it possible to take the largest cross widths of two or more sails and use these to create dimensions for a ‘virtual’ sail that is recorded on the certificate?

For boats certified to the 2002 CR, no. The Ten Rater class rules I.2 and J.2 refer to the measured rig area and measured sail area of the largest rig. It follows that the largest rig and sails to be used shall be presented to the measurer and be certified.

The Ten Rater class rule does not require that the largest rig and sails be used at any event. However, alternative sails are mentioned in Section C and in order to certify those sails the measurer shall check that they fall within the profile of the largest sails (the dimensions of which are recorded on the certificate). This check cannot be made unless those largest sails are present.

For boats certified to the 2016 CR, yes. The concepts of measuring the largest suit of sails and alternative sails having to fit within the profile of those sails no longer apply. It is possible that the dimensions of 'virtual' sails could be placed on the measurement form and sails checked against those dimensions for compliance.