An electronic fuse (eFuse) is a device contained within the CPU, allowing m$ to make changes to the values of these fuses, resulting in different/controlled operation. With the janurary update, they "blew" an eFuse (personally, i think they change the value of it), which results in slightly different encryption of your onboard NAND (kernel, dashboard, key vault, etc...). This allowed them to prevent people from using a pre-4552 kernel (one that is exploitable). However, if you removed a resistor and disable the eFuse power supply, they could not change, or blow, this efuse. Thus, people are able to use both an exploitable and a current kernel on the same system.
So, if they do a kernel upgrade that requires the eFuse to be blown, those who have disabled the eFuse power supply could possibly have a fragging system, or one that will not update.
Caster.