I have a question about changing traits on moribund cards.

Say I have in play Desert Exiles, which has the text " Response : After a Reinforcements card is played, draw a card." I also have a Maester with a Copper Link attached. For some reason, my opponent decides to play You've Killed the Wrong Dwarf! on my Maester, which kneels him. I trigger the response on the Copper Link and add the trait Reinforcements to You've Killed the Wrong Dwarf! Do I meet the requirements for triggering the response on Desert Exiles, or do I not because You've Killed the Wrong Dwarf! was not a Reinforcements card when it was played? Can I even add traits to events in this way?

Another example might be that I have a Maester of the Sun (with a Copper Link, and it's summer) out with at least one other character, and my opponent plays Valar. Maester kneels to save himself, I trigger response on Copper Link to turn another character that was just killed into a Sand Snake. Assuming I can pay the cost, can I play No Use for Grief from my hand, triggered off this new, dying Sand Snake ? Or was it too little, too late for the Sand Snakes to not grieve over?

From the FAQ (p. 25); tells you everything you need to know to answer your questions:

"Can I trigger The Dreadfort (Dreadfort Betrayal 105) when I play a Bolton Refugee (Refugees of War 83) with a printed STR of 2, and have Winterfell Castle (Core 25) in play, which gives the Bolton Refugee +1 STR?

Qualifying characteristics of cards are checked at the time a Response effect is triggered. In this example, the Bolton character enters play and has its STR raised to 3 (by the constant effect on Winterfell Castle) when it enters play, which occurs before the Response effect is triggered. When the Response is triggered, the character’s STR is 3, and it has just been played, so you can use The Dreadfort to draw a card."