Warrant canaries haven't been tested in court. (They have been used as notification of an NSL though.) In particular, judges are human beings, not robots, so the laws are interpreted and implemented by humans. Because they're not robots, removing a warrant canary toes the line on communicating to the affected, in violation of an NSL. Thus, removal of the canary most likely means an NSL was received, but the canary staying up doesn't necessarily mean that there wasn't an NSL. Lawyers at every organization have considered the situation and advised their client, but those lawyers are not at the FBI.
I don't think you're meant to remove warrant canaries when you get a secret court order, you're just meant to continue renewing your warrant canary at a regular interval as long as you don't get a secret court order.
My understanding is that they can prevent you from removing warrant canaries but they can't force you to continue announcing "I have not received a secret warrant".
But the FBI could advise the canary poster that not continuing to post the canary notice could lead to legal action (esp. since that person has willfully put him/herself into the situation). Then it would be up to the recipient of the NSL to decide if it’s worth that risk, which is as stated above, untested. It’s a fine line between telling them to lie versus telling them the ruse could be in violation of the gag order.
Conceptually you can't because you can put as a citizen any requirement to make a canary that the law cant compel you to do. For example, you can pay to publish the canary: the state can't compel you to spend money on it. Or you can make a small petty crime with it (say, an IP Violation).
In places where there are limits to what the government can do to an with you, its possible to resist.
Why are you arguing about what is conceptually possible? The reality is such that people can absolutely be compelled to lie in public, especially for "national security" means. It happens all the time. Failing to update could signal something, but continuing to update means nothing. "Resistance" and other such concepts don't hold up to scrutiny against shareholders and 40 year sentences.
The constitutionality of whether the US Government can force someone to update a warrant canary has never been tested. Until it is, it’s foolish to declare with certainty whether it is or is not legal. We can only speculate at best.
We know that the legal bar for forcing someone to speak or not speak is high (compelling state interest), but national security has usually been held to pass such a bar.
