Modern high performance CPUs/SoCs do not contain flash, ever (the processes are incompatible). When we talk about SoC fuses, we mean real fuses (or antifuses), not the Flash "fuses" of some microcontrollers (which can be erased with UV light).

Actual technologies vary. It could be fuses (metal, polysilicon, or other) or antifuses (e.g. gate oxide breakdown, "blown" means it conducts), but they're all irreversible.