I've been thinking about this. Sure, some characters are omnipotent, and others are aware of the fourth wall (did they ever decide whether or not Pinkie Pie knows?), but how did Gaspode find out in the first place? Was he just there? And once the PPC knew about that, why didn't they decide to neuralize him? I had an idea for an agent getting in trouble for revealing the existence of the PPC to some ^Lyrical Nanoha^ characters, but I've been driving myself crazy trying to figure out why they wouldn't be able to neuralize them in that situation. I was thinking that it would be a one-off gag anyways.

There are a number of different calibers of "awareness", and most of them would actually be counter-productive to what the PPC tries to do. We protect the plot without forcing ourselves on it, in part because letting the canon characters know of the existence of the multiverse would alter the path of their story and in part because projecting oneself onto a world that was doing fine without you is what the Mary Sues do, and we don't want any part of that. That's why we neuralyze people, and why it's frowned upon for the PPC writers to introduce new characters with knowledge of the multiverse unless there's a good in-universe reason, i.e. the character in question is omniscient and would know about it anyway. It's not good for main characters to start expecting and recognizing PPC agents, or it runs the risk of Sueishness. It's one thing to team up temporarily with a canon character to drive off an intruding presence, and another entirely to start striking up friendships with people from other universes when said other people have their own narratives to attend to.

The "deja vu" idea is close to one of the passable types of awareness, where a few characters, such as BBC Sherlock, will gain limited knowledge after they have been fully replaced, restricted to the basics like knowing they've been separated from their world and shoved in a plothole before, and that someone fixed the problem when they experienced it last time. They do not gain full knowledge of the PPC(though Sherlock occasionally manages to deuce the scope of what it is and what is going on while he's still in the plothole) in part because the canon snapback will return them to their previous states and in part because they're neuralyzed to forget any information from accumulating. However, none of the Fellowship apply for that state. It would take a particular mindset, the sort of mind that can prodigiously analyze patterns and simultaneously allow for the most wild of possibilities to be accepted as potential reality, to apply for that state. Hence, BBC Sherlock.

Some of the Lord of the Rings characters have other states of awareness, with Gimli having a sort of OOC avoidance since the badfic writers tend to ignore him, and Elrond having an active OOC resistance thanks to his ring's protective magic(by that logic, Gandalf and Galdriel would have it as well, since they have the other rings in Elrond's set, but I don't think that's ever been addressed), but neither of those types give the user knowledge of the PPC. They just leave them aware that something strange is going on, and the characters begin to want no part in it despite being forced along in the wake of whatever is corrupting the canon.

Namely, Galadriel, Elrond, and Gandalf. All three are highly intelligent, perceptive, very old, and wear rings of power.

They still go OOC--especially Elrond--but they fight against it. I would expect them to occasionally have the presence of mind to actively help the agents once they realize what is going on, because they are more resistant than the average canon, and catch on to things more quickly than the average person. They are all resistant to corruption and, more importantly, wise enough to know they are not immune.

Eru Ilúvatar, like all omniscient deities, is OOC-immune and knows about the PPC. He's probably the only one in Middle-earth who is always aware of the PPC's actions. Other canons, even very powerful ones, probably only get vague hunches that those frazzled people in the weird black uniforms are trustworthy. Perhaps PPC agents look foul and feel fair? :P

Maybe they might have a weird feeling about it, like deja vu