Could I post something like this to a thread where an article behind a free registration screen is being discussed?
Sure, though you get no bonus points for stating the obvious.
What we want to discourage here is the use of anonymizers and the like. You can do that as much as you like, just not here.
So: “You can discuss lying to them, but not ways to make that lying a little easier.” Is that the ruling?
How about posting a valid userid/password pair?
You mean that there are people who provide accurate data when registering on sites like that? I had no idea!