“I don’t wish to continue this line of discussion in this thread but will be glad to in a different one that is more subject specific.” - No problem, stating personal preference.
*“You may not discuss this further in this thread on penalty of official sanction.” *- Junior modding.
Things in between are context dependent. Generally a poster expressing their own desires without hint or implication they are imposing or enforcing some rule on other posters is okay. Even making requests is perfectly acceptable and common,* “can we keep this thread about red hens, and not yellow or white ones, please?”*
In the thread in question, it’s fine for **Superdude **to express his desire to not wish to participate in a discussion about certain aspects adjacent to the thread topic. I’d say a better practice if he wished to avoid a certain line of discussion is to mention it once and follow through with that, but it’s not a rule violation in that instance to mention it a few times as he did, based on my reading.