If there is a conduit, you would have no access to it at a random spot in the middle. You may be able to pull a new cable up a stepped mast using a fish-tape, but only if there is a junction box or something at the base that you can open.
I put my radome high up on the mast, using the steaming light weldment as a cable exit point, and have since regretted it. (Windage, big blind spot.) And yes, I had to cut and splice the cable to get through the deck. It probably causes some signal degradation, but I have no way to measure that. Also, the supplied Furuno cable is barely long enough to get to the base of the mast - fortunately that's where my chart table is - but there's nothing left to run aft from there to more common locations. I understand that modern radomes have much simpler cables, so this may not be as much an issue these days - basically just an Ethernet drop. And there are wireless options too.
If I started over again, I would probably go for a stern-mounted pole or arch mount. Maybe even a backstay mount. Although in those cases, one has potential interference with solar panels or SSB antenna. But it's not a big enough issue to put effort into changing it.