Answer to "What part of my display got damaged?"I have a MacBook Air 11” and mine also had these marks, but i took the whole display apart and it looks like the bottom led’s that illuminate the panel are broken (those are soldered to the lcd sheet) you are better off replacing the lcd assembly completely and that’s it. Sorry.
Answer to "Internal display cable replacement"Its not that hard... i just replaced an lcd a few days ago and while it's not the same repair you're asking, i had to replace its cable too. Not hard at all. Just be careful.