Need advice on replacing 100amp main lighting breaker in a pushmatic- live panel involved in diy
If doing this first turn the breaker off or all of the loads on the breaker (yes I understand it’s still live).
Using the proper gear electricians do this all the time. I would add a face shield just in case. I have to wear a green one that I think makes it more dangerous because it makes it harder to see (a few years I started using an auto darkening welding hood it covers the face and is clear until a flash).
If I remember the screws on the pushmatic are captured so you won’t drop the screws, if they are not this will be the dangerous part of the job removal and installing the screws. I carry a small jar of rubber cement, some times called contact adhesive. I dip the screwdriver tip (a proper screwdriver will be a snug fit without the glue) let the glue dry only takes a minute. Remove the screws. The contact adhesive is sticky and helps hang onto the screw if it is not captured.
Dropping the screws can cause a short that may end in a arc flash.  The protective equipment is there for this possibility on top of the live circuit.
Wear cotton clothing nothing that can melt.
Use caution, loads turned off, face shield, gloves, insulated tools and heavy cotton clothes and caution while doing the work.
Just to make clear the loads are turned off so when the screws are loosened there is no arcing while coming out if the breaker is stuck on. Make sure the new breaker going in is off so it doesn’t arc on contact.
It has been quite a few years since working on a pushmatic I think the screws are captured but may be wrong the rubber cement although can be messy can be a real aide on the tip of the screwdriver