Yeah, but he does continue to believe that he'll go to hell for doing it, because (in his mind) it's still objectively wrong to let a slave run away. He isn't suddenly against slavery, at all; he's against Jim being a slave, because he knows him as a person. And even after all that, after how well Jim treats him, after they bond, after he decides he's a person, Huck lets Tom talk him into leaving Jim locked up in a cell just so they can spring him, when they could just go and say "Hey, he's been freed, he can go", because it would be more fun. They keep at that for several chapters, because it's a game to them. The freedom and life of a fully grown man, but it's more fun to let him suffer. And Twain wrote this, with no implication that Tom and Huck were in the wrong.

And this, from Chapter 32 of the book, quite a bit after the "I'll go to hell then!" epiphany, Huck to Tom Sawyer's aunt:

"It warn't the grounding -- that didn't keep us back but a little. We blowed out a cylinder-head."

"Good gracious! anybody hurt?"

"No'm. Killed a nigger."

"Well, it's lucky; because sometimes people do get hurt.

Not even counting a black person as a person in a story Huck's made up. So. Yeah.