Flamestrike got there first, but this is what I was going to point out.
And that is close enough to cannon for me.
I am down with allowing Demons or Fiends to redeem themselves. It is a terribly long and difficult road of course.
I don't think I would allow aberrations though, especially the more other-worldly they are. The more the mind becomes an alien intelligence or more instinct, the less the prime material planes' morality will be apart of said creature.
And I also think using your character's strength of will and conviction to change the laws of the universe to allow Fiends or Demons a chance at redemption is a cool story worth telling! Certainly something I would allow if a player came to me with the idea.
You'll have a hard time convincing me that these scenarios are not PR.
And what makes the second scenario more compelling is that scenario B involves actually seeing a Vrock demon doing good works, while scenario A just involves someone claiming to be an ex-demon. Seeing is believing.
It is simple: PR that no one sees or hears about isn't effective PR. So, the onus is back on you: Where are the vrock helping old ladies cross the street and getting cats down from trees? Are the murder hobos so thorough that the Gooders won't let them out (in which case, PR failure)?
And again, you can ignore the ancient red dragon in the room, but how much work does Good have to do to get people to not run away when they see the fiend (unless of course it is a succubus/incubus, but that is a different problem), so the general public can see the reformed fiend?
I'd speak to the DM to see how they feel about what is possible, what is not, and whether attempting to redeem a devil is plausible and worth the while. I always thought Crowley from Good omens might be an example of a redeemed Devil, not totally "good" but not actively evil at least during the book.
Unfortunately this class also requires the rest of the players (not the PCs) to be in on it enough to let foes live long enough for it to be possible.