1. If person expressed pigul intent at one step but expressed that he does not have a pigul intent at a later step, is the pigul intent negated?
2. Why isn't the rule as follows: the pigul intent is established if expressed at any relevant step unless and until it is expressly revoked at or before the last relevant step?
Dear Leonard,
The answer to question 1 is that the Pigul remains and is not negated. There is no Derashah on your idea and there is no mention of this in Shas or Rambam. The Kohen, when thinking (speaking) wrongly is like breaking a glass; it doesn't help to regret it later. It's true that Kares, if one eats it, happens only at the last stage (if no other thoughts mix in), but it's already ruined, the Korban is Pasul, from the time of the Machshavah.
As far as question 2, it's a nice idea but the Torah sets the rules, and here the later "revoking" has no effect.
All the best,
Reuven Weiner