To see how easy it’ll be to replace the cable, give it a gentle tug from above and see if you can see it moving down below - this will be easier with two of you. If you can, then securely attach a piece of string to the end of the cable in the cabin and pull it up through and out of the roof. Once you’ve done that you can use that pull-string to pull through any new cables.
The 2A 12V feed will just be for the aerial amplifier which you probably won’t require if you replace the broken flying saucer with a decent log periodic.