While theoretically possible, they haven't been made due to the fact that mostly SX users, which are the minority, would be affected. Also note that installation has nothing to do with the bricking process. Installing the brick .NSP files isn't what caused the brick, it was launching the files. Remember that .XCI and .NSP contain the same contents but are just utilized differently. They only differ in the way they are packed; they are just containers of .NCA files.
.NRO files are homebrew applications and you should already know where these go if you have been using Tinfoil which is a homebrew application. Games installed to the SD card are located in the Nintendo folder.
The only purpose of downgrading is for accessibility for future exploits because the current exploit is firmware agnostic.
Maybe try using another source and/or CFW.
That's fine. Boot0/boot1 only change when AutoRCM is enabled, when EmuNAND is installed, or when your firmware changes; no other changes are recorded in the boot0/boot1. If your current firmware doesn't match the firmware of your rawnand, you will need to make a new set of boot0/boot1 that does match the firmware of your rawnand with
ChoiDujour. If you don't know what firmware your rawnand is, you can check it with this
tool.