Opposite of invariant

I look for the opposite of "invariant" in the context of scientific language. If you look at this example sentence:

[...] Although it is translationally and rotationally invariant, it is not permutationally invariant. [...]

There is a repetition of the word "invariant" and a double negation. ("not" and "in-" as prefix)

Since I could not find any example of people saying "variant" for "not invariant", I do not know how to nicely write this sentence.

If I look at Merriam Webster and list the possible antonyms:

changing, deviating, nonuniform, unsteady, varying

I think none is fitting, but I am also not of English mother tongue.

Variant is correct. It can function as an adjective meaning essentially "having variety", and it fits here as "invariant" is also an adjective.

As for why this is not a common use, I can't say. It's perfectly correct and has an appealing familiarity to it. If you're looking for advice relating to the jargon of a specific field, I suggest you consult experts of that field.