I am no pro but I would get a piece of PVC pipe and cut a channel down it’s length and replace or cover the metal pipe one with it if you get large enough PVC pipe. I would take a couple ring clamps and tighten the fuck out of them to “close” the channel you created. My way would make it so you don’t have to disconnect the wire but still kill the breaker.
Yeah, I was originally thinking along similar lines of cutting a channel lengthwise down a pipe just enough to fit the cable through. Then closing the opening with caulk. But since I do have easy enough access to the top already, I think I’ll just slide it down though the top