My pleasure.
First, I use this -
https://play.google.com/store/apps/details?id=nextapp.sdfix - and if you read the full description there, you'll nearly be an expert on the whole permissions thing, he really did a great job.
As for the second part, here's an example.
You have your music downloads - Amazon, home rips, whatever - and right now, they're in some folder or folders. And you have album artwork, not embedded in the music files (for lots of reasons). The artwork may have come from an app, here's one that I use -
https://play.google.com/store/apps/details?id=com.citc.aag
Next - your music player wants to see the artwork and songs in the same folder for each album. How to do it? Grab X-plore, make a new folder for that album - copy over the music, copy over the artwork. Now, X-plore owns that folder. Point to it with your player (it's not going to write anything) and boom, now you see your artwork with your music. Then using the original apps (if not rooted) go over and delete the originals so you don't duplicate space. Pretty sure you can do all that from your PC too. (But it's been too long for me to guarantee. I think so, but now I do everything on my phone.)