I have a better idea.
Make the checkbox say "I have read the Forum Rules", and then link to the
Unofficial Rules thread.
All this is in an ideal world. I know of many cases where users do not read the terms of the financial contract, rather than the rules of the regular forum. Almost on a daily basis, we have those who complain about casinos or exchanges, but in fact, they only refer to their own ToS, which everyone accepted during registration.
I believe that at least 50% of members do not know what OP_RETURN is, and even if there was a warning that it is not allowed to write about it, they would certainly accept that rule, because they don't know much about it anyway. It's not their business.
Logically, if someone hears about the term 'mixer' for the first time during registration, there is very little chance that they will go on to fully educate themselves about it, just to better understand the registration conditions.
According to the sample from the alternative forum, it is surprising how many people have no idea about what, how, or why mixers work. Even if they have been in the mixer sig campaign for a year.
In the end, it is no longer forbidden to talk about mixers, only mixer advertising is forbidden.