I’d like to do change the height of the railing with GH. But when I set the component, the railing disappears from the viewport. Please tell me what I’m doing wrong.
which is deconstructing the default options and reconstructing them with only the height being changed with a slider.
Your approach does not work because you are trying to set custom options, but the component remains orange which means it does not have all the necessary inputs to compute, so then in turn the railing component fails too, again orange meaning missing input data (if there was red anywhere would mean error in input data and/or calculations).
So if you indeed want to define custom options and not only change height, you need to provide all inputs to the railing options component, specifically the railing style S which is empty by default, and/or the other too according to your preference.