To my knowledge it's not possible to directly apply measures to Design Alternatives created using the Create From External File
button. Any measures attached to these OSMs will not be applied during a PAT run like they would be in OS.
The only way to apply measures to an external file is to attach them to the baseline/seed OSM in either the OS or PAT Measures tabs. These measures will be applied to all Design Alternatives including ones created from external files. Alternatively, you can use the Apply Measure Now
feature in OS to incorporate measures into the external file before attaching to the PAT project.
So in your (reverse) case with the proposed model being the baseline in PAT and your baseline created from an external file, you'd have to first apply the the Rotate Building Relative to Current Orientation measure to the baseline and save as a new OSM and then bring each rotation in as a new external file.