It is crazy difficult to get your components to stay where you want them if two different type of components fail at once.
I've made machines that are dozens of chunks big just to reload a reactor from scratch quickly, just so that the components are in order.
I think my suggestion will make "fun" reactors easier. Also, doesn't it make sense to be able to prevent people sticking heat-sinks into the fuel rod slot? :p
My suggestion is maybe add an option to lock slots so they only accept certain components.
That or make a block that can feed components to a certain slot(s?) in the reactor inventory(or maybe any inventory) only.