I do not work in a nuclear plant but I imagine that the locking out mechanism could be too complex ?
Maybe it is something they should remedy and have a classic override switch nearby for workers ? Maybe they deemed that this would cause other safety risks in case of mistake and maybe that’s why they didn’t put such a mechanism. Then maybe you could just have a light nearby to tell if the mechanism was overridden so workers could check visually ?
Anyway, since I never worked in such a facility I have to trust @Superlyte27
Can you imagine a simple system, and how it might go down if someone were able to just throw a switch that cooled a reactor. If the pumps aren't on, the core will melt. So, jerk off gets mad at the world, throws a single switch and a reactor melts. I'm just being paranoid. But, seems possible.