How to change this code to insert lines if missing without deleting existing ones

tie my @lines, 'Tie::File', $fn or die "could not tie file: $!";          
    for (my $i = 0;  $i < @lines; $i++) {
        if ($ln_title == 0) {                           
             if ($i < $#lines and $lines[$i] =~ /(\s+TRACK \d\d .*)$/) {         
                 $lines[$i+1] = '    TITLE ""';
             }
        }
   }                      
untie @lines;