The gemara learns out from the pasuk of "lo yechashev" that aside from the issur to eat pigul, there is a prohibition on the kohein against creating pigul by having a thought of eating the korban outside of the proper time (or burning the eimurin on the mizbei'ach after the proper time). However, whether or not one would receive malkus for creating pigul would be dependent on whether there would be malkus for a לאו שאין בו מעשה. We pasken that there is no malkus for a la'av sh'ein bo ma'aseh so the kohein doesn't receive malkus for creating pigul. Nonetheless, the sefer ha'chinuch (mitzvah 144) writes that it isn't counted in the taryag mitzvos because it is under the general heading of the la'av of pigul (which is the prohibition to eat pigul).
We've mentioned before that there is a machlokes whether pigul is created by the kohein merely thinking to eat it outside the proper time, or only when he verbally articulates it. The Mishneh l'melech (pesulei hamukdashin 13:1) cites a machlokes between tosafos and the rambam about this issue. The magi'ah on the mishne l'melech asks that if pigul can be violated by merely thinking without articulating it verbally, how can there be malkus - how would he be warned against pigul? The Minchas Chinuch says that he doesn't understand the question because even if pigul can be violated without verbal articulation, the case of malkus may be only when it is verbalized. The minchas chinuch himself asks the opposite question. The gemara implies that pigul is a לאו שאין בו מעשה, but according to those who say that it can only be violated through a verbal declaration, it should be considered a ma'aseh since the declaration results in a consequence of establishing pigul? Just as the Rambam (Issurei Miz'beiach 1:2) writes that one gets malkus for being makdish an animal with a mum because through his speech the status of hekdesh falls on the animal, here too through his speech the status of pigul falls on the korban? The minchas chinuch explains that according to those opinions that anything that can be violated without an action, even when it is violated with an action, may qualify as a לאו שאין בו מעשה and there is no malkus, all is good. But according to the opinions that it can only be violated through a verbal declaration, and according to the opinions that when violated through an action even if if could be violated without an action it deserves malkus (and certainly according to the rambam in sechirus who holds that even when violated without an action, there is malkus for any la'av that could be violated through an action), why is it considered a לאו שאין בו מעשה?
Perhaps the concept of an action resulting through a statement would only apply when we consider the statement to be creating the status such as hekdesh to a ba'al mum. But here by pigul the status of pigul is not a direct result of his actions rather the din torah is that when one has a thought of חוץ לזמנו the torah places the status of pigul on the korban, we still consider it a לאו שאין בו מעשה.