The process for sysNAND is fundamentally the same except that you're putting a different fw.img on your SD card and you are making a copy of system.xml before you change the default title ID, renaming it syshax.xml, and pushing it to the same directory that you will place your modified system.xml. I'm not sure why the pull system.xml from "/vol/system_slc/config" instead of "/vol/system/config". Not saying it's wrong because I have no clue. I pulled "/vol/system/config/system.xml" for coldbooting sysNAND.Below is a guide specifically for sysNAND coldboothax. One thing it doesn't mention is disabling standby and quick start prior to modifying your system.xml. I think if you have quick start enabled you will brick your box. Not sure about standby but I wouldn't recommend testing it. Follow the steps and do a triple sanity check prior to pushing your modified system.xml to the Wii U.Even if you're coldbooting redNAND you'll be fine unless you go out of your way to paint yourself in a corner. The lastest Haxchi installer by default will get you a Haxchi'd title that boots fw.img by default and boots homebrew launcher if the A button is held down. So if it wouldn't matter if you didn't have a usable fw.img. You could hold down the A button and it would boot sysNAND and launch the homebrew launcher.