As I said below, I copy the record numbers (using the copy/move/change tool) to replace the label field and then append a prefix and suffix to them (to make them unique as I find labels are often treated as “contains” rather than as “is” fields by the temporary citation matching - although they may have fixed that).
then change temp citation in preferences to use label rather than the record number. I have also used the pages field instead, which doesn’t require regular copying.