Is there a word to describe "one who is in passive opposition to an established order or government?"

I think you want

dissident noun a person who strongly disagrees with and criticizes their government, especially in a country where this kind of action is dangerous

Oxford Advanced American dictionary

dis·si·dent n. One who disagrees; a dissenter.

thefreedictionary.com

Consider satyagrahi in the sense of passive but 'constructive' opposition

an exponent of nonviolent resistance, esp as a form of political protest

although Gandhi did not strictly coin the term satyagraha to mean passive resistance, it has come to mean nonviolent resistance in a broad context, and he was himself given to using the terms interchangeably.

A close term that would fit your context I think is meliorist.

This is a conscientious objector, in many instamces