Kir Kanos: When do you use his ability?

Does this happen during the "Modify Attack Dice" step (rulebook page 11) prior to rolling defence dice?

That looks like the logical place to activate his ability. I see nothing that suggests the attacker can spend a token at any other point in the process.

Adding die results to your attack roll goes in the "Modify Attack Dice" step of the attack sequence.

"Modify attack dice" includes either of Rerolling, Changing and/or Adding results.

This is one of those cases where it's easy to over-read what rules the ability is overriding.

There are fixed windows where the attacker's dice can be modified. Kanos' ability doesn't do anything to change that window, so you're still bound by it even though you can spend unusual tokens in unusual ways.

Got this one wrong myself at a first pass

Thank you all for the answers.

That being solved, one or two additional questions arise:

1) How exactly do you "add 1 hit result to your roll"?

Do you pick up a physical attack die and place it next to the other three (or four at range one) dice?

2) If the answer to 1) is that you add an actual die, is the attacker allowed to re-roll that extra die after adding it? This question assumes that the attacker has a target lock on the defender or that Howlrunner is nearby. (Why you would want to re-roll a hit is not part of the question.)

No, it is not a physical die. You place the evade token there to indicate the hit. It acts just like an evade token during an evade roll, but in reverse. It can't be rerolled or modified. It counts as an extra hit result. It can be cancelled by a evade result or evade token as normal.

You can represent it however you want. The official rules suggest using the token or an unused die, but even if you use a die, that doesn't make it a "die" that can be rerolled or otherwise affected. It's a hit result, nothing more.

Yeah you can track it however, but as Buhalin said, it's kind of a 'phantom' result, and even if you track it on a physical die, it is not a die result and cannot be treated as one for rerolling, modifying dice results, etc.