What? You can't say "call me they/them," rather you can only say "don't call me him/her/or any other pronoun besides they"? That's very silly.
Clarification of rules, even to the point where they may seem redundant, is completely fine and often important. This is such a weird hill for them to die on.
The new rule is not a clarification of the existing rule. If you'd not like me to call you "OP", that's fine, I can refer to you by your username or they or I can refer only to "the post", and if you prefer a pronoun, Cellio states she will use that pronoun. The issue is that the new rule states you must use a certain term whichever the user specifies.
Clarification of rules, even to the point where they may seem redundant, is completely fine and often important. This is such a weird hill for them to die on.