If the topic post of a topic gives very specific rules for the topic, I will use those rules in addition to the global board policies for that topic. The starter of the topic may not change rules after posting their topic (not even by editing the topic post). Local rules can't specify punishments, though people may be banned for breaking local rules too much.
The rules must be specific enough that it takes less than a few seconds to decide whether a post breaks them. When you report posts like these, you must quote the local rule that was broken. Rules will be ignored if they are not specific enough, or if it takes too much work to enforce them.
It is possible for someone to create a "ruleset" that others can quickly apply to their topics by clearly linking to the ruleset.
(It has always been my policy to enforce local rules, though not many people have created topics with such rules.)