"Should I do that as the series progresses and add codes as the content becomes heavier?"

In my opinion only the codes describing the most critical aspects of one's story shall be used. But if you want to tell the reader that later parts are heavier and thus the uploaded story changes its codes over time, try this: Use all codes right from the beginning, that's better than fumbling them in later on. Then use your synopsis to explain the planned course of your narration, just as you did above.


"not serious and not hard enough for heavy"

So you are stuck between "seriou"s and "heavy"? Without having read the story, I cannot say much about this, the more so as this point strongly depends on personal judgement.


"forced to excrete without privacy"

Well, that's a horse of a different colour. Since faeces are not directly involved in a sexual act, it is not scatology per se. But even so it might be necessary to use this code as a warning. Again: It depends. If the scene in question is like that -- "She was not allowed to clean herself with anything other than ice-cold water, had to eat from a dog bowl and shit in the garden." -- then you are safe with "humiliation".