Hi,
Maybe that is what you are looking for:

Code:
# data
$original_string = "33445566";

# test
my $result_string = my_convert($original_string);
print $result_string;

# the function for string modification
sub my_convert(){
    my $var = shift;
    my $new_str = "";
    foreach ( $var =~ /.{2}/sg){
        $new_str .= "0x$_,";
...