You can mastic over the cut between the two holes to reinstate the ip rating. it only needs to be a saw blades width. what is it with using stuffing glands on a cu?? just clip the cable and use a blind grommet with the correctly sized slot made in it. I really do hope you have friends who will carefully check your work, it's what you dont know that can be dangeous, not the things you are unsure of! BTW if they are going to sign it off, it most certainly isnt legitimately just so you know, however this behaviour does go on and it is frowned upon by anyone with a concience.