my @records = split(/^(?=I)/m, $file);

##</code><code>##

my %pkg_lkup (
   ... => ...,
   ... => ...,
   ... => ...,
);

for my $rec (@records) {
   if ( my ($refdes) = $rec =~ /REFDES=(.*)/ ) {
      if (exists($pkg_lkup{$refdes})) {
         $rec =~ s/PKG_TYPE=.*/PKG_TYPE=$pkg_lkup{$refdes}/;
      }
   }
   print($rec);
}

##</code><code>##

$rec =~ s/PKG_TYPE=\K.*/$pkg_lkup{$refdes}/;