Any government which exercises de facto authority is entitled to the respect due to that authority. They thus have the duty (and right) as the ones in power, to do the things that must be done, for the running of the country. They can collect taxes, maintain the roads, regulate trade, defend the borders, etc, all for the common good. If a government is overthrown by violence and a new government is imposed, which has the effect of replacing a good (or less evil) government with one that is more anti-Catholic, it is entirely moral to contemplate counter-revolution, overthrowing the revolutionary government by force. However, all such considerations are subject to the Catholic doctrine on Just War. The proposed counter-revolution must be winnable, and must not result in more suffering for the people than would result from enduring the bad government. All of this is a bit vague, but in practical terms there are some examples we can use. For example, the Spanish cινιℓ ωαr was a "winnable" counter-revolution by the conservative, Catholic military, against a new government which was very leftist, strongly sympathetic to, and eventually openly allied with, the Soviet Union. On the other hand, in the US, even though our government is technically "revolutionary," there is no popular and military support for a real counter-revolution, and so such a war would not be a real war, but an ιnѕυrrєcтισn, which everyone would justly condemn as "domestic terrorism." Thus, for a Catholic, it would be immoral.