Exodus as justification for political or religious terrorism?

To the insane and mentally unstable or those they have terrorized or brainwashed, you can justify almost anything. I will take up this part of your question:

How would you explain Exodus to these extremists so as to discourage this kind of justification?

First, Moses, Aaron, and the people of Israel DID NOTHING except believe (and paint their doorposts with blood). They did not cause frogs to leave the river or the sky to turn dark at midday. God did those things.

“It is mine to avenge; I will repay,” says the Lord. (Romans 12:19)

Thus I would say, believe all that you want that certain forceful practices against unbelievers are justified and call on God to do them - but leave it to Him. It is not your place to do those things.

It is true that the Egyptian priests and magicians duplicated the first few signs. Given that, the initial assumption of the Egyptian people was that Moses was personally performing these miracles, hence was responsible for terroristic acts. But as the plagues worsened, even the religious establishment in Egypt was forced to conclude that it was not the work of a man, but a god.

Second, this was not a war (not until Pharaoh sent his army to march against them at the Red Sea), so talk of "just wars" is not relevant. Each plague either had as its agent a creature or force of nature that was worshiped as an idol by the people of Egypt (like frogs), or caused the death of something they worshiped (like cattle). Each plague was an example of God saying, "This is not a god, this cannot save you, so do not worship it." All the people of Egypt worshiped these idols, except the Hebrews, and I imagine many of them did as well (as the Golden Calf episode would attext), and were forced to make a choice. Thus all the people of Egypt were guilty of idol worship and were deserving of punishment. God in his mercy slowly increased the severity of the plagues, giving them a chance to abandon their ways. It was not a war - it was a judicial action by God, the judge, against individuals, and every Egyptian was individually responsible.

Third, The Hebrew people's action was to insist on religious liberty - the right to go into the desert and worship their God. Theirs was a legitimate act of civil disobedience against a genocidal empire that had tried to kill all their male children. When a state commits genocide, the people who are being killed or enslaved have the right to self defense, and the genocidal actor loses all legal right to govern them. Thus the actions by Egypt to suppress them are not legal, because they constitute a continuation of the genocide.

Terrorism: The unlawful use of violence and intimidation, especially against civilians, in the pursuit of political aims.

It was Egypt that had been carrying out terroristic actions against the Hebrew civilian population in the pursuit of political aims, not the other way around.

Fourth. One cause of the judgment was ingratitude. You might say, but how were the Egyptian people to know that they were worshiping idols? They were just following their leaders. The telling detail was that years before, God used Joseph to save all Egypt from a famine, and the people chose to forget that deliverance and not continue to show gratitude to the one who saved them or the people who kept alive the memory of that God.

God is one to show leniency in proportion to ignorance. The people of Egypt were not ignorant, so they were not innocent. They were guilty. When confronting people, you must likewise show restraint. How much has the witness of God's truth come to a people or a person? That must temper your approach when speaking up for the truth.

The article The Ten Plagues and the ethics of modern warfare, while not explicitly using the term terrorism does interpret this portion of Exodus as making a case for following just war guidelines and only using a 'nuclear option' (all first borns killed) as a last resort.

So that's at least one example of Exodus being used to inform posture, policy and strategy in modern warfare.

Are there any Christian denominations which in fact consider terrorism to be justified?

Perhaps no denominations properly speaking, but definitely there are some Christian individuals and/or groups that do so.

Christian terrorism comprises terrorist acts by groups or individuals who profess Christian motivations or goals. Christian terrorists justify their violent tactics through their interpretation of the Bible, in accordance with their own objectives and world view. These interpretations are typically different from those of established Christian denominations.

These terrorist acts can be committed against other Christian denominations, other religions, or a secular government group, individuals or society. Christianity can also be used cynically by terrorists as a rhetorical device to achieve political or military goals.

Christian terrorist groups include paramilitary organizations, cults and loose collections of people that might come together to attempt to terrorize another group. Some groups also encourage terrorist acts by unaffiliated individuals. The paramilitary groups are typically tied to ethnic and political goals as well as religious ones and many of such groups have religious beliefs at odds with conventional Christianity.

Religion can be cited as the motivation for terrorism in conflicts that have a variety of ethnic, economic and political causes, such as the one in Bosnia. In cases such as the Lord's Resistance Army or the Taiping Rebellion the beliefs of the founders differ significantly from what is recognizably Christian. In such cases the term Christian terrorism is problematic despite the claim that they are motivated by their religious beliefs.

Numerous individuals and groups have cited their Christianity or Christian beliefs as the motivation for their terrorist acts. This can mean that they see Christianity as their identity, partially in comparison to another group which they view as threatening and non-Christian. Terrorists can also cite their interpretation of the Bible or Christian beliefs as their motivation.All types of terrorism have a complex interrelationship with psychology and mental health, however only a minority have diagnosable medical illnesses. Christianity can also be disingenuously claimed as a motive to inspire followers or curry political favor or protection. All these motivations are not independent and often complexly interwoven.

Christianity came to prominence in the Roman Empire during and directly after the rule of Constantine the Great (324-337 AD). By this time it had spread throughout western Asia as a minority belief and became the state religion of Armenia. In early Christianity there were many rival sects, which were collectively persecuted by some rulers. There is, however, no record of indiscriminate violence or attempts to use terror as a religious weapon by early Christian groups.

Once a particular Christian sect or creed gained state backing religious violence increased. This took the form of persecuting adherents to rival Christian beliefs and other religions. In Europe during the Middle Ages Christian antisemitism increased and both the Reformation and Counter-Reformation led to an increase in interdenominational violence. As with modern examples it is debated as to what extent these acts were religious as opposed to ethnic or political in nature. - Christian terrorism

I can find no denomination that openly justifies terrorism through interpretation of the Bible. However there are individuals and Christian groups (sometimes within a particular denomination) have done so.

See the following article for more information:

Modern Christian Terrorism (page 29)

Inside Terrorism (page 116) Religion and Terrorism