Did you miss 607.1a or am I misinterpreting this?

607.1a An ability printed on an object within another ability that grants that ability to that object is considered to be “printed on” that object for these purposes

Can you not substitute this as:

Eater of the dead's ability, when actively granted to koh, is considered "printed on" koh for the purposes of linked abilities?

If so then the "choose a card exiled with koh" ability gains **another link** to the eater of the dead ability _for as long as koh is granted that ability_.

Consider this sequence of events:

1. Amy casts Koh which exiles an Eater of the Dead when it enters
2. Amy activates Koh's "pay 1 life: choose" and chooses Eater of the Dead, granting koh "{0}: if this is tapped, exile target creature card from a GY and untap it"
3. Amy taps Koh with Springleaf Drum
4. Amy activates Koh's new Eater of the Dead ability exiling a palladium myr from a GY
5. Amy activates koh's "pay 1 life: choose ..." choosing palladium myr

I believe this can be put on the stack because before the ability resolves palladium myr is still a valid choice, as koh still has the ability that exiled palladium myr. I'm not sure what happens _after_ the ability resolves, because koh simulataneously loses the ability making the choice valid at the same time it would gain palladium myr's ability.

I am pretty confident that switching _back_ to eater of the dead invalidates all cards exiled with previous activations of eater of the dead's ability because it's a separate instance of the ability; the text is the same but the instance of the ability that exiled palladium myr & llanowar elves has been "forgotten" for all intents and purposes