There are various ways to look at this, but they all boil down to "technically, yes":
From a domestic law point of view, the country's Constitution, written or unwritten, will likely have definitions of how power is transferred. That might be "elected by universal suffrage", or "whoever inherits the Crown has absolute power", or it might include multiple bodies holding each other in check. However, Constitutions can always be changed, either within their own terms (e.g. passing an Amendment in the USA) or simply by force (pieces of paper don't protect well against tanks). So, first you declare absolute rule, then you sell that absolute rule to the highest bidder.
From an international law point of view, things are actually pretty similar. There may be Treaties that you would have to break somewhere along this process, but just like the Constitution you just ripped up, they're only as strong as anyone willing to enforce them. If the country was a member of the EU, for instance, it would certainly be kicked out for violating the relevant treaties; but that wouldn't stop it being a country.
This leads on to the subtler question of international recognition. Other governments, and international bodies like the UN, might declare your rule "illegitimate", and might even go so far as to recognise some opposition organisation as the "real" government. They might impose sanctions of one sort or another which would be inconvenient; they're quite unlikely to actually invade. In practice, there are plenty of "illegitimate" governments which so clearly are in control of countries that the international community has no choice but to deal with them as such. It took twenty years, but the UN eventually reassigned China's seat to those with de facto power.
Which brings us, finally, to the internal reality of the country. If you have absolute power, you can declare that every piece of land, every factory, everything in the country, is now your personal property. If you already control the military, the government, and the judiciary, there's nobody left to dispute that claim. The reality on the ground will be that you can control and exploit those assets at will, unless and until someone challenges your rule. Whether you acquired that absolute power by birth, violence, or buying it from someone else, makes no difference that I can see.