Major renovation of historic landmark building

Hello I am working on the major renovation of a historic landmark building in part of an area protected as world heritage site by UNESCO, and the building cannot be modified in its envelope since the structure is a load bearing wall building dating back to the 1890's. For energy performance doing the energy modeling, is there an exception for having to compare against a baseline with envelope materials as described in 90.1 as these would be impossible conditions since the envelope cannot be modified