Ivan,
first of all, I don't see why you would want to do that, taking into account that you can distort the connection between comments and rung completely in that way. I know it was possible in S5. It was even possible, if you had a lot of idle time, to edit an S5 program without the Step5 software simply by editing the hexadecimal values on the diskette. But both were dangerous things to do, especially if something went wrong you were in a huge pile of s**t.
As far as I know you cannot edit the rung comments separately from the program in S7, which is a good thing if you ask me.
Kind regards,