A Mitzva's Mitzva
The well-known phrase in the Torah that prohibits "Meat in Milk" is LO T'VASHEIL G'DI BACHALEV IMO. (No, this is not yet the Mitzva's Mitzva; this is the mitzva chosen as an example.) Usually, translated as Thou shalt not seethe a goat in its mother's milk. Bad translation, because G'DI is more inclusive than just goat, which is G'DI IZIM, in the Torah or EIZ. G'DI is a generic term for the young of farm animals - calf, lamb, and kid. And worse than a bad translation is the distortion of the Traditional meaning of G'DI in this phrase, which is - the meat of cow, goat, or sheep. Worse yet, is the distortion of the second part of the phrase by the straight translation.

CHALEIV IMO means the milk of cow, goat, or sheep, regardless of any relationship between the source of the milk and the source of the meat. It gets more complicated (as is well-known, but we are reviewing the topic before we get to the "Mitzva's Mitzva". The phrase appears in three places in the Torah: Mishpatim, Ki Tisa, and in this week's sedra, R'ei. The Oral Law teaches us many things that are not obvious from the Written Word. 
Here are some of the facts about Meat in Milk that we know from the Oral Torah. 

The first appearance of LO T'VASHEIL teaches us the prohibition of COOKING meat and milk together, regardless of purpose, or even for no purpose. The act of cooking the two together is a Torah violation.

The second time we have LO T'VASHEIL, we learn the prohibition of eating of Meat-in-Milk mixtures that were produced by cooking. Beef Stroganoff, which involves cooking meat with sour cream and other ingredients, may not be prepared by a Jew, AND the resulting dish may not be eaten BY TORAH LAW. It is vital to point out that even though Beef Stroganoff (for example) does not fit the literal definition of G'DI BACHALEIV IMO, it is no less a Torah violation than poaching baby goat meat in its own mother's milk. Not one bit less. The prohibition of eating Beef Stroganoff is NOT a Rabbinic extension of the Torah's law; it is within the definition of what G-d prohibited with LO T'VASHEIL. Eating is part of the definition of LO T'VASHEIL. Sour cream from the milk of a cow that was unrelated to the cow from which the beef came from, is part of the definition of G'DI BACHALEIV IMO. 

The third occurrence of LO T'VASHEIL in R'ei, teaches us that the prohibition of eating Meat-in-Milk includes deriving of any benefit from the cooked mixtures. This too is Torah law no less than the prohibition of cooking or eating. Feeding your dog from a can of dogfood that contains beef and beef byproducts, milk and milk byproducts (I've seen such dogfood) is a Torah violation on the same level as the aforementioned baby goat meat poached in its own mother's milk. Not Rabbinic extension or legislation, but Torah Law.

In addition to transmitting to us the Oral Law, our Sages also legislated and extended Torah law. Eating a sandwich made of alternating slices of glatt kosher salami and chalav Yisrael cheese is forbidden by Rabbinic law, although the Torah does not forbid it. Cream of chicken soup that involves real chicken and real milk is forbidden to eat by Rabbinic law, but not by Torah law. (Preparing it for a non-Jew is also permitted by Torah law, and the Sages did not forbid the cooking of fowl and milk either (only the eating).
All of the above was a review of a particularly interesting set of prohibitions, in order to set the stage for a discussion of "a mitzva's mitzva". Actually, there are two that will be presented together as opposite sides of the same coin. This pair of mitzvot are from Parshat R'ei too. They are known as BAL TOSIF and BAL TIGRA, the prohibitions of adding to or subtracting from the Torah (and her mitzvot).

And here will not be a lengthy treatment of the "obvious" violations of these prohibitions. A person who adds a fifth species to the Lulav & Etrog set - for the sake of the mitzva - or takes only three. Most commentaries say that BAL TOSIF or BAL TIGRA are violated only with an act. 

Rambam defines them as including a halachic ruling of a qualified authority which in essence adds are detracts from the Torah. According to Rambam, if a posek were to say that Beef Stroganoff is forbidden to eat (correct), but that the prohibition is Rabbinic (wrong), he would be in violation of BAL TIGRA. This is a significant ruling, because even though the Rav in question insists correctly that one may not eat the food, his claim that it is less than a Torah violation is in itself a violation of this mitzva's mitzva.

One more step. And this is the main point of this piece. What if you or I THINK (feel, believe, even lean towards) that salami & cheese sandwiches are prohibited by Torah, or that the Torah only really forbids "in its own mother's milk"? Or that it is the Sages who ruled that driving a car on Shabbat is forbidden, not the Torah? Or that something that is a CHUMRA (a strict measure) is actually forbidden by halacha? Are these too violations of Bal TosifF or Bal Tigra?

It seems that these would not be actual violations of the prohibitions. (For a posek to say so would itself be a violation of Bal Tosif.) But it can be suggested that there is a violation of the spirit of the prohibitions of Bal Tosif or Bal Tigra. Even if a lay person's thoughts are not in the same league as an act of adding or subtracting to mitzvot. Even if one's thoughts are not like the psak of a halachic authority, there is still an element of distortion of the Torah (even in one's own mind), which is the essence of BAL TOSIF and BAL TIGRA. Thinking that the Torah only prohibits "in its own milk" and that the Rabbis added the rest, is a distortion of G-d's words. So is believing that the Torah prohibits chicken with milk. Again, even if the requirements of halacha are maintained, there is still an element of distortion of the Torah which is bad, and potentially worse.

This is especially so in light of our roles (even as laymen) in the transmission of Torah to the next generation. Each of us is a link in the Chain of Tradition, and we teach our children not just the do's and don'ts of Judaism, but the thoughts, feelings and attitudes as well. Therefore, what is probably not an actual violation of Bal Tosif or Bal Tigra, might nonetheless be responsible to a corrupted picture of Torah. 

The Midrash tells us that after G-d told Adam that he may not eat from the Tree of Knowledge of Good and Evil, he transmitted that Torah law, so to speak, to Chava with an addition - that we may not touch the tree either.

When subsequently, says the Midrash, the Serpent enticed Chava to eat the fruit, he used Adam's distortion of G-d's word to his advantage. When Chava realized that G-d did not forbid touching the tree, she proclaimed that EVERYTHING her husband has told her is a lie. Had Adam suggested not touching the tree as a safe course of conduct, that would have been fine. That would make it like a rabbinic rule. Our commitment must be to the package of Written and Oral Law and Rabbinic Law. But we must know and appreciate the difference.