Yep, you're right, it will be possible to get the cable moving again and if it wasn't possible to get a replacement or I needed the car moving asap, then I'd also free it off. I've done exactly that with an old MR2 going in for it's MoT test and probably even the Europa over the last 30-odd years.
But it doesn't last because if it's rusted the galvanising will have gone on the inside of the bowden cable and sod's law is that it's in the middle where you can't see. You can pour oil in or even molten waxoyl but the chance of 100% rustproofing is low, so it's going to go again.
The best you can do is remove the cable and soak in oil but if you use the car regularly or in wet weather then it's only a matter of time before you're going round the loop again. A new cable is £55-ish, not cheap I grant you, but I suppose it's how much value you put on your time to remove/soak/free/replace. The handbrake is lousy but it's the only emergency brake you've got so it might as well work.