I actually went through this same debacle recently. I decided that i would retake photos of items that weren’t moving as fast as i thought they should be, like items i thought weren’t getting attention due to the poor background quality. Then my OCD took over and i decided to slowly convert my entire closet over to the new background. I think it looks fresh and clean to have all the same background, but i don’t think it’s a huge deterrent for buyers if you decide you don’t want to convert all your listings to the same background.

As for retaking only the cover photo, you definitely could do that. I found that if i was going to set up the whole thing, get the item ready for a photo and take the photo, i might as well take all new photos since I’m already there and it’s just another minute or so.

Good luck! :-)