Those who turned back from the rebellion against the Valar were pardoned, and the Doom against them lifted.

I understand.

If it's killing the innocent that earns this... could you you Doom orcs, or does this only work on people fighting against the Enemy? Even better, could you Doom him?

If they came to Valinor and spilled blood on its shores.

The Enemy did spill blood in Valinor.

The Enemy is Doomed by forces greater than our own.

Yes. Yes he is. If God won't kill the devil, then Man will do it.

I'm sure we agree on hoping that doom reaches him quickly.

That is not how things are fated to transpire.

Then–

Wait, the contents of fate aren't secret?

They fall on deaf ears if the hearer should not know them.

Is it known what the criteria are for who should know what?

Elves cannot have information that would change their course. Men I do not know of.

Would you like to find out whether the same is true of Men?

It would be hard to know the difference between 'Men can have information that will change their course' and 'you will not have the opportunity to achieve such things'.

If there is anything fated to happen soon, that would otherwise be easy to postpone, or fated to never happen even though it sounds achievable...

Fates are for major things. 

...it is possible that you have already averted some.

My arrival certainly did, but as far as I know that wasn't because of an action I took...

How would it have been caused by you but not by an action you took?

It would be caused by whoever or whatever brought me here.

Were there others that I may have averted?

Fëanáro was doomed to die very early in his futile war.

Oh.

It still is early, as Elves count it. It might take a long time before we can be sure fate has changed.

Indeed. The war is fated to go on for nearly sixty Years.

Sixty–

Do you know how early Fëanáro was to die, or how?

I do not. 

So we can't easily find out if humans are exempt.

I could decide to spend the rest of my life in Brithombar if the next piece of fate I hear has an even number of words, and Tumunzahar if it's odd. Then hearing it should change my course no matter what the content is. Would an Elf who tried that be able to hear the prophecy at all? I'd have to pick something I don't mind actually doing, of course...

If both of the courses committed to were ones that the Elf was not fated to take, then yes, they would not be able to hear any future prophecies.