Andrew

Welcome.

That's a characteristically full, helpful, and expert view from John.

I'd just add another plug for Chris Thrale's very good book.

Never cock a taploader with a pellet in the tap. The risk is the pellet seals the transfer port, and so when you fire there is almost no air in front of the piston. Which is a bad thing.

On point 3, I wouldn't do it either, but the safe option would be to try de-cocking while firmly holding the lever with the tap open. Never tried it myself though.