I would say more than a focus on the status quo, the key to pinpointing the Protagonist or Antagonist is to really nail down the source of Conflict at the Concern and Issue levels, and the static plot point of the Story Goal. Once you know for sure what inequity you’re dealing with, it becomes clear who is pursuing or avoiding the Goal that’s tied to them.
Keeping things the same might not always be clear in a narrative depending on the Mindset and how closely a story even adheres to the concepts of Protagonist and Antagonist.
That being said, I second that checklist @mlucas laid out… look at the Protagonist and Antagonist in terms of the Initial Story Driver (and also the Concluding Driver).
Adding to that, another factor I think about it is that the Initial Driver puts a StoryMind at rest out of whack; brings attention to the Mind that an inequity exists.
Once that Driver disrupts the mind, there are two forces at play from an Objective POV: One force that sees a target which would bring that inequity back into balance, and a force that wants to avoid and/or prevent the inequity from coming into balance. For good or bad, that second force is basically okay with the inequity, or the perspective is that it’s not so big of a problem that there is motivation to pursue the Goal.
Compare it to a Steadfast character. It’s not that there is no inequity for an Antagonist, it’s that there’s a POV which is OKAY with the inequity. In Back to the Future, the Steadfast MC perspective describes the dilemma of a situation in which on one hand, one shouldn’t put themselves on the line in order to stave off future rejection. But at the same time, one should choose to be open-minded to realize their full potential.
It’s a bit of a hypocritical place to be coming from… but the subjective stance is that it’s okay to be in that place. Marty represents this perspective in the storytelling, and we see that not only does he live with that duality unmoved, it’s his unchanging source of drive! An opposing POV might influence Marty to realize that he’s a bit of a hypocrite… and it does! From the IC POV… but it only serves as motivation for him to stay the course (not unlike a Protagonist vs. Antagonist).
There’s a great question on Subtext that asks if the MC’s personal issues slow down the plot or not… and in that sense, you can almost see certain MC’s as mini antagonists to their own Protagonist (which in most cases is the same Player).
@jhull’s recent update to The Matrix points out that Neo’s issues slow down the plot. If the Goal is Obtaining, breaking free… and Neo as MC has to balance his self-doubts with his personal truth. Neo as MC almost the dynamic of a mini Antagonist for a while. (Of course the MC is not tied up in the OS, but just using the forces at work as a comparison).
So, I’m not sure it’s so cut and dry in terms of keeping things the status quo… and likely why there’s debate over James Bond and the like.