Hello Russell! You can run the export once at 1:100, drag that drawing into your set… then export again at 1:50, drag that drawing into your set. It is not possible to run multiple scales for the same drawing in one export.
I think the default behavior is to show all scales in the export. You could probably get into LayOut, delete the imperial scales you don’t want… close everything… re-open. Let me know if that works!