Does a modifier before a conjunction like `and` apply to both the subjects of `and`?

I would say that if someone is intending parallelism, and fails to clearly indicate that, then that's on them. If we read it as "a work is classical by reason of its resistance to contemporaneity and its resistance to supposed universality", we are taking "resistance to" to be implicit. So if I have absolutely nothing else to go on, I would go with whatever has the least parallelism, as that adds the least to the text. Using this rule, someone who want to have the modifier apply to both can explicitly say so. If we were to take modifiers to always apply to both, then a writer who didn't want the modifier to apply to both would have a difficult time writing the sentence accordingly.

However, it is common for people to employ parallelism without being conscious that they are doing so (for instance, people will put if a == b or c in a program expecting the computer to interpret that as if (a == b) or (a == c) and being confused when it doesn't), so this will often result in not interpreting the sentence according to what the writer intended. In spoken English, there can be differences in prosody that can distinguish between them.

In this case, "contemporaneity" refers to a particular time, and so is the opposite of universality. So it's logical to conclude that "resistance" refers only to "contemporaneity".