That is a very good question without an easy answer. From my personal experiences, in most cases I would agree that no PPE would be required. However, several years ago I was an industrial electrician. One night I was troubleshooting a lighting circuit when I thought that I saw a little puff of smoke coming from the transformer bank that fed the panel that I was looking in. I proceeded to remove the cover from one of the still energized transformers. As I eased the cover off, some grit that was inside shifted and the transformer blew up in my face! The arc blast knocked me back some 15 feet!
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My hope is to replace this with a rebuilt DS switchgear with a DS secondary main breaker. This will limit arc flash energy into the feeder breakers to a safe level.

We have multiple substations that don't have secondary mains and have primary fuses. All are over "40 cal". It's a huge problem for us and we can't seem to adress it quickly enough.

This is an iffy subject. Other things come to mind such as, opening an MCC 480V bucket to reset an overload or to test for voltages. There are no physical alterations being done, only inspection. I suppose you could shake some dust loose or accidently have your meter in current mode instead of voltage mode when measuring. I wish there was a more finite line drawn for these type of scenarios. Common sense is to don the ppe.

I would say no ppe. There are two things that come to mind now that may change that though.
1. Are there any switches, meters, etc. mounted in the door that may have wires pull loose when opened
2. Now that the door is already opened and I see an overload etc. that needs to be reset am I now going to take the time to don ppe

Thanks for giving me some clarity on that. What about simply reseting a breaker or an overload with the door closed?

The purpose of opening the door in my senario would be to attach a remote actuator, just a magnet that sticks to the metal breaker front panel. The breaker would be open or closed wirelessly from up to a couple hundred feet away.

In that scenario, I would call it "working on energized electrical conductors and circuit parts", and refer to Table 130.7(C)(9).

Article 100 defines "working on (energized electrical conductors or circuit parts)" as Coming in contact with energized electrical conductors or circuit parts with the hands, feet, or other body parts, with tools, probes, or with test equipment, regardless of the personal protective equipment a person is wearing.

In the photo it appears that something is energized as I see a digital display illuminated. I cannot comment on the video at this time as my company blocks Youtube.

I figure that in the best case (depending on how you look at it), the line side terminals on that breaker are energized. Opening the door could (Low risk I admit) cause conductive grit to become dislodged and cause an arc flash/blast.

You asked for opinions in this scenario, I'm merely providing my opinion. I am not OSHA, therefor I cannot provide you with a formal interpretation. I am only stating how would handle a similar situation for the 120 maintenance electricians that look to me for guidance. Yes, I will err on the side of caution. Yes, it may be inconvienient, but explaining to family members that their loved one is hospitalized or worse is a far worse inconvienience in my opinion.