Oh, and since I already got one PM about it, I might as well post it here.
There a three things that will majorly affect what you can do without causing massive instability and nasty events. The first being your government type. For example, if you are a monarchy, you can change policies and/or political parties whenever you want (with some negative affects, but at least you can do it...right?). But on the other hand, if you are a democracy of some type, the only way you can change these is through elections (that you don't really have a say in (I say really because there are ways to sway votes)), but you're people will generally be happier. The second is, well, political parties. Whatever your ruling party is will put restrictions on what you can do. For example, if you have a more "conservative party" in charge, then you can only raise your taxes to a certain point, but if you have a more "liberal party", you can increase taxes higher than that of the conservative party. In addition to that, whoever controls the upper/lower house or the higher/lower courts will affect what laws are formed/passed. If you try to pass a "conservative" bill with a "liberal" controlled upper house, then it will probably get rejected. Thirdly, is laws. Laws you can create, or the upper house can create, that affect your country and may affect what leaders can and cannot do. For example, the United States Constitution will not allow the President of the US sign in his own laws, just as an example.
But all that aside, you may ask, "well it sounds like I won't get a lot done", which is absolutely not true. You have to play with politics, manipulate your way around the political stage. You are the country, remember. So you could tell me to have the courts review a law, or have the upper house form a law, or have the leader propose a law to the upper house, what have you. They may not always work, as I explained above, but you can still do it. If you don't like someone in office, have one of the political parties attempt assassination. Like I said, you control the whole country, but things may not work or go as desired based on several factors... (Like if you tell me you want farmers to riot over the lack of education, its probably not going to happen...)
I hoped that cleared things up. This may not be the final product just yet, but it is what I'm going for.