modifying it means I need to retest it on *all* the inputs.

This should be trivial to do. One file full of input strings and one full of their expected results.

while (my $input = <$testInputsFH>)
{
  my $result = doBigRegexOn($input);
  my $expected = <$expectedResultFH>;
  warn "Test failed; got $result instead of $expected on line $.\n" un
+less $result eq $expected;
}
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