my %date_convert = (
    ...
    'Dec 29' => '04-12-29',
    ...
  );

##</code><code>##

  my $day_re = '(?:Mon|Tue|...|Sun)';
  my $mon_re = '(?:Jan|Feb|...|Dec)';
  my $time_re = '\d\d:\d\d:\d\d';

  $text =~ s/$day_re ($mon_re \d+) ($time_re)/$date_convert{$1} . "_" . $2/ge;