The variable is when one thing can be stated in an infinite variety of ways and as such is subject to the fallacy of equivocation. Any underlying law, expressed through the variable, is the equivocation of one law in a myriad of ways.
Not clear why variability implies an infinite number of ways, nor on why this infinite number of ways makes a variable subject to the fallacy of equivocation, for an equivocation arises when there is a conflict in meaning between two or more expressions. Boy, I am tired! can be either an address to a "boy" literally, which it usually is not, or it can be a rhetorical "boy" used idiomatically. Put these two in a context where implications are drawn from the one referring to the other, and you have your fallacy.
The "underlying law expressed through the variable" being an equivocation itself is curious. The underlying law is, you might say, only as good as it can be expressed as a law, i.e., in language, and language is always, already ambiguous in the given "variable" of its utterances, awaiting for context to make the meaning clear. No language concept or proposition is stand alone, but requires context, usually so generally assumed that no one questions this and it seems like what is presented is stand alone, but this is never the case. Thus, if I can try to understand your point, the variability of the expression of the underlying law itself does need context, as all good variables do, but if this is true for all discussions about underlying laws, then this variability never leaves our descriptions of the world, even when we go deep into the most general level of assumptions.
The paradox is Heidegger's hermeneutics where this circular thinking is actually embraced, for there is no foundation beyond what language can produce, and language is contextually restricted. The "myriad of ways" is a reference to the matrix of alternative contextual possibilities, and you are in Derrida's world now.