use Fcntl               qw( SEEK_SET );
use File::ReadBackwards qw( );
 
my (@lines, $loc);
{
   my $bw = File::ReadBackwards->new($qfn)
      or die($!);
   @lines = map { $bw->readline() } 1..9;
   $bw->readline();
   $loc = $bw->tell();
}
 
{
   open(my $fh, '+<', $qfn) or die($!);
   seek($fh, $loc, SEEK_SET) or die($!);
   truncate($fh) or die($!);
   print($fh "abc\n");
   print($fh @lines);
}