So in order for me to update my sysMMC without burning fuses, what I do is download the system update in "OFW" by booting Stock mode via Hekate then I delete my Wi-Fi settings, reboot back into CFW for sysMMC, and install the update. You should also have AutoRCM already enabled before installing the update in CFW otherwise you will just burn the fuses. As long as you have AutoRCM enabled, you will never ever use the official bootloader unless you accidentally perform a system update outside of CFW (it happened to me one time by accident which was my own fault).
As for when the system dies if AutoRCM is already installed, it will stay there so you don't need to worry about re-enabling it. For more information on AutoRCM, I wrote an entire thread about it which you can find
here. I should also reiterate that what I am doing is out of my personal volition and the fruits of my research from following the banning situation (I made a thread on that too by the way). You do not have to feel forced to follow my advice if it doesn't interest you or not safe enough.
Is the SD card formatted as exFAT?