IANAL, but I'd think that hurting your possible future defense is what you just said, and what people always say: that the premeditated intent is to violate a p

IANAL, but I'd think that hurting your possible future defense is what you just said, and what people always say: that the premeditated intent is to violate a potential future gag, and that removing the canary (or not updating a cryptographic signature, or resetting to 0 the "__ days since last served a subpoena" notice) is a mechanism for that violation. IMHO, that's kinda a weaselly trick, no matter how good the cause, and it might not stand up, not legally, nor in extra-legal practice.