Generally (setting aside cases of a "davar charif" -- spicy thing) if one cooks in a pot that is not "ben yoma" (i.e. they cooked milk in a pot that was used for cooking meat more than a day ago) and is clean then the food is permissible b'dieved (after the fact) since we say the taste inside of the pot that will come out is already "nosain tam lifgam" (gives a bad taste) and won't make the food not kosher.
This is all of the person unknowingly cooked the food in such a pot. However what about if the person knowingly cooked the food in such a pot. Normally we say don't cook in such a pot because of a decree lest you come to cook in a pot that is "ben yoma" and will prohibit the food. However if someone purposely took a clean pot that was cooked in it meat over a day ago and now cooked in it milk, what's the halacha? Do we say that since the taste is no longer good then we'll still permit the food. Or perhaps there will be some sort of "kanas" (fine) for doing this and we'll still prohibit the food.
I'm asking this question after having been inspired by the following. There is a Taz in YD Siman 122 who brings from the Darchei Moshe that brings from the Hagos Sharei Durah that if a Jew doesn't know if his cli is ben yoma or aino ben yoma then we give him a kanas and consider the cli as if it's ben yoma (there is much discussion on this Taz including those that argue.) Perhaps this case is much different however it's still that of some sort of "kanas" (fine) being imposed even when there might not be any taste in the pot that could ossur.