Yeah, I have a manual that specifically states:
"...HELPFUL HINT: The bolster clean out screw on percusion rifles can be removed for easier cleaning. If this is done, be certain that the screw is cleaned separately before being installed."
That said, on THAT rifle (bought within the past year), the cleanout screw is ridiculously easy to remove, and I usually do. However, on most of the older ones that I have, the screw is, as you said, now nothing more (or less) than a plug, probably forever "one" with the bolster. I know for certain that an old CVA pistol that I've had since around 1980 has a cleanout screw that used to be tough to remove, finally one time around 1989 it was so hard to remove that I ruined the head. I just left it as it was, tight in the bolster (it never even loosened a tiny bit), then I filed off the marks from me messing it up, polished it and it looks great that way. Not removing that screw changed nothing in the way the gun cleans up.
I am no expert at all, in anything, but I figure the gun is the final say in whether that screw comes out or not. We all do what we do, not much will ever change that. As for me, I leave the ones that are a pain to remove, and remove the ones that act as if they were meant to be removed. So, that's about all I can say.
And as far as "experts," I agree.... there are two kinds of "experts," the one we're all familiar with is spelled "e-x-p-e-r-t," and it is used to indicate a person that possesses an advanced level of skill, knowledge and understanding regarding a given subject, far above that of the average person. The other is spelled "x-spurt," wherein we all know from mathematics that "x" is an unkown quantity and a "spurt" is - well, we all know what that is, too, so it really means "an unknown drip under pressure." Of course, too, an "expert" has at different times been defined as a man in a business suit carrying a briefcase, 50 miles from his home... where SOMEONE just might have a higher opinion of him than do those with whom he is well acquainted!
Anyways, maybe I am an x-spurt after all. Who knows... works for me.