TMC works with every NC now that we know what files are required, however on some NC's the old V13 receiver (and older) are not fully working anymore.
Affects not all devices and changing the NC often works fine.
You'd have to update your bootloader for SDHC support but for the NC you should be fine.
You don't go back - you make a backup using Windows Explorer (NOT TT Home!), that's called a backup ;)
If anything does not work out you delete all files and copy your backup files on the device, all back to the old.