Okay, years later I am reading this thread (while stuck in Paperspace hell) hoping for an easy way to accomplish exactly this in Acad 2023 (full version).
No easy way, this still being (2023) Paperspace hell BUT while in PSpace looked into my Layer Properties Manager AND right after Color there is a heading called VP Color, so I figured why not give it a try? Since there appears to be no easy way to Select All (that I can find, is there?) in the Layer Properties Manager, I started at the top, held the Shift key down and scrolled (and scrolled...got a lot of layers), selected Black, closed out, regened. All my layer in viewport are Black, so yay! My MSpace layer colors stayed the same, the PSpace layers have no line weight, but who cares? I can at least see the drawing in that viewport...gonna find out if I have to do this for every viewport...if so, will take less time to copy that one viewport and pan/zoom as required.
...Okay just tried copying the viewport with the all black layer colors...but the colors changed to MSpace colors, but I clicked inside that viewport and regened...and they changed all to Black. So yay!...Oh wait, that's not what happened. Now I can't figure out what I did to get all the layer colors to be Black in Pspace.
Okay, just figured it out - while in PSpace I went into Page Setup Manager, changed Plot Style Table to monochrome.cbt and below that checked"Display Plot Styles". Closed, clicked on each viewport, switch to MSpace, regen. Viola! All black lines...but I have to regen every viewport, even if I copied the previous all-blackline viewport.