GOOD NEWS! I can confirm that you can update through system settings here is what you need to do (and after I Can explain how i "safely tested this before doing it"
0.backup nand and boot and store on pc
1. have your sx dongle plugged in, as well as the rcm jig
2. boot up
3. go to system settings and start update
4. This is key watch closely, as soon as the update is done (or just before) hold VOL +
* you don't need to hold power just vol +
5. the system will auto reboot and due to jig and VOL+ it will go into rcm despite not pressing power (cool right)
6. when sx menu comes up reinstall rcm autoboot
7. boot fcfw
You should now have 5.1 or whatever you just updated to with auto rcm protecting you and fuses intact. I compared my fuses using other payload to be sure.
oh so how I figured this out:
I disabled rcm autoboot, and tested to make sure it wasn't there
then while powered up I put the jib and sx pro widget in, and held power button till power menu came up and I clicked restart and immediately held vol+ and the sx menu booted up, basically proving the power button was not necessary and that all that was needed was vol+ (and pin 10 grounded) at start up or even restart. Not only that I tested this with a charger too. YOu know how when you plug in a powered off switch it turns on, so I tried it with jig and plugged into my computer while holding vol + then with tegra rcm smash loaded a payload and it worked (no power button necessary)