Why would you need to redraw the linework?
I mean I assume you were drawing in the way that it was supposed to look in-game.
If not, then you'd have to redraw anyway, even if this wasn't for Spine. There's no really workaround for that.
But as mentioned, you can use high-res textures in Spine and then just export the lower-resolution textures from there.
There's also no problem with working in Photoshop at 200% or 400% the intended game size. I think that's pretty typical.
But you would also typically export that scaled down before using it in Spine.
You could still use the original resolution in Spine but it would be a bit inconvenient as you'd keep zooming out and, depending on the computer you use, might be more of a video memory hog to work with. And, again, you'd have to see how the scaling down of the textures on export affects the tolerances of the parts based on the art style.
I'll see if @erikari or @shiu has some recent tips on how to handle resizing a skeleton if you've already created it.