I'm not specifically familiar with the raptor, but yes drain cables can be replaced if you can gain access to the routing usually thru the bottom.
Take a good look at the bottom cover and see what you need to remove to gain access.
Last year I replaced 2 of 3 drain cables on ours as the cables had plastic selves and they broke at the mount right behind the handles.
After unbolting around the outer edge and looking where everything actually was, I had to remove a hose carrier, 2 brackets on the LP line, then make 2 cuts in the cover to remove a section of it, as the whole cover was 6' wide by at least 8' long. Only needed access to about a 1' x 4' area right inside the frame. Just don't make any cuts in the cover without looking inside first as the valves probably aren't exactly where you would expect. And there may be wiring or plumbing laid inside it.
After getting access, you can search EBay for the length(s) you need. The outer cable is usually clamped to a fixed part of the valve, and the inner cable will fit in and have a bolt crimping it to the valve slider.
It will take a bit of contorting your arms/hands if it is anything like ours, but you can do it.
2004 Colorado 35RL
2005 Ford F350 Dually