my $line_number = 0;
foreach my $row(@content){
# count the current line number
$line_number++;
# remove the newline
chomp($row);
my $rowsaver = $row;
if($rowsaver=~/^\d/){
  # curent row starts with a decimal
  # no extra action required, just process it 
}else{
  # ok, current row does not start with a decimal,
  # we need to add a newline to the output file
  # before we process this line
  print $fh "\n" if $line_number > 1;
}
:
rest of your code
[download]

So you can rewrite that code as:

my $have_to_newline = $rowsaver=~/^\d/ ? 1 : 0
print $fh "\n" if $have_to_newline && $line_number > 1;
[download]

This approach works, except for the first line, if that does not start with a decimal, then your output file will start with an empty line. that is why the if $line_number > 1; is there in the first example.