awk '{$2="#"$2;print $0}' your_file
This will add # to the start of the second (space-separated) column regardless of which position it occurs at.
sed -r -e 's/^.{15}/&#/' file
Insert '#' in position 15
Creating a .pem with the Private Key and Entire Trust Chain Log into your DigiCert Management Console and download your Intermediate (D...