I think in this case it's upscaling that will butcher video quality. But please, try it out and see if it works for you. And please let us know how it turned out.
For my YouTube retro gaming videos i always upscale to 1280x960 or so to avoid compression artifacts. I haven't tried with artificial scanlines though. I use Kdenlive for editing and rendering. You find my MSX videos here Patrik's Retro Tech
I made a test with OBS and could capture the scanlines (20%) in openMSX (great, did it!). Thanks everybody...
Thalin, have known kdenlive for a long time, time I polish my skills at editing video if I want to record a great video with MSX game...