Wellll, in Europa Universalis 3, there is a bit of Holy Roman Empire sim going on, but nothing extremely deep. I am aware that there are some mods in the work for the game that try to improve the HRE's interestingness.
But, in general, Paradox Interactive has been pretty keen on this. Trying to dramatically change your country, go to war on whimsy, attack everything in sight whenever the opportunity is presented is Punished. HEAVILY. In the Heir To the Throne expansion pack for EU3, there are three different statistics, Infamy, Legitimacy, and Stability, which operate in different ways to make ruling your country hell if you do it in a way that upsets, the international community, your citizens, or the Status Quo.
Usually, it is never a good idea to accept even a small stability drop (It's on a scale from -3 to 3,) and a drop of 3 or more can be disastrous. This can happen if you declare war on neighbors you have good relations with, without a good Causus Belli. such as them occupying land you have a legitimate claim on. That sort of thing. Revolt risks skyrocket when it dips below zero, you get fewer merchants, your tax and trade efficiency drops, and your Legitimacy drops.
Infamy is a score that starts at 0 and can reach arbitrarily high levels. If it goes above a certain limit determined by how good your leader is at diplomacy, and other factors, then every country in the word gets free reign to invade you for being Dishonorable Scum.
Legitimacy is something that only effects monarchies. As it drops, the morale of your troops declines, revolt risk rises, Pretenders to the crown start trying to take it from you violently, and other monarchies that have a royal marriage to your family can try to take your crown by force due to you lacking a decent claim to it.
Generally, it is a bad idea, very bad idea, to just be a prick to the world in EU3.