I find unclear the way the two lists are interleaved. In a style similar to that hinted at in GrandFather's comment, I'd tend to write this as list of hashrefs:

my @TEST_REC_PACK_FIELDS = (
  { name => 'status', data => 'n' },
  { name => 'time', data => 'n' },
  { name => 'date', data => 'N' },
  { name => 'code', data => 'a16' },
  { name => 'msid', data => 'a10' },
);
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At this point you can just as easily construct the list of fieldnames and the unpack string, but it is more self-documenting, and you can easily extend the structures later if you need to start adding validation callbacks and the like.

Hope this helps,

Hugo