Don't think the scratches would come back as it seems the color blends in with the scuff's. I just used a some what soft wash cloth that was rather old and in the "throw away" pile. After you wipe off all the excess and make sure it's all gone you can keep using the cloth around the area and even a small amount of distilled water seems to do the trick. Though I haven't been able to get the shine completely to go away yet but I actually like it a bit shiny as many parts of the car seem to be as shiny especially with lighting. I also didn't see any paint rubbing off after drying the area (cleaning with a clean cloth) so I'm not too worried about it.
I did notice that using double sided tape on some soft packing sheets didn't really hold so I just taped the hell out of it under the shell so I can put the shield on without fear of more scratches, seems to work really well. I for the life of me don't know why this wasn't done the first time. Seeing that large batwing made me some what want one in 1/6 but after this crap from HT I am really really on the fence about it.