That’s a good question. I’ve had that question for some time.
Obviously, this kula only applies where something is muttar meikar hadin. When someone accepts a chumra in kashrus, they can choose to accept it only for the item itself, not keilim, for the simple practical reason that accepting it for keilim is potentially a bigger hardship, because it means not eating in others’ homes even if they would buy the foods you accept.
That part I think is clear, but the question remains whether there is a halachic way to distinguish, aside from the practical non acceptance of the chumra in certain cases.
I think there is, perhaps, based on how blios work. We never really know for sure when or if the blios are nosen ta’am into the food. To illustrate, if we knew for sure that the first time you cooked in a treif pot all of the ta’am went into the food, it would be muttar to subsequently use that pot. The reason it’s assur to use the pot a second time is because we are choshesh that the ta’am didn’t leave the pot the first time.
So, although obviously we asser pots which are balua even with an issur d’rabonon, perhaps on a chumra, we can be someich that the pot wasn’t nosen ta’am to the food.