Yes, as long as you make the source available to customers under a GPL-compatible license (i.e. with no restrictions on their modification or distribution), you can charge whatever you like.
Though it only takes a single buyer publishing your changes to potentially undermine such a business model.
I think Red Hat’s approach is that they will refuse to sell you any more versions if you do that. I’m not sure if I like it or not.
Not sure how they'd enforce that since you can republish anonymously. Also not sure how the various CentOS alternatives that have popped up in recent years would work in that case, they'd need to find a new person to buy it every time there's an update.
With CentOS, Red Hat pulled a cunning move: they started supporting the project themselves, then after some time changed its direction from a repackaged white-box Red Hat to a fast-moving prerelease Red Hat. Now it's much harder for a bigger business to decide which of the CentOS-lookalikes to choose.