Lukashenko is a dictator. Being able to change laws at a whim is a defining characteristic of dictatorship.
* power delegated to the President by statute passed by Congress
* powers explicitly and exclusively delegated to the President by the Constitution (of which there are few)
It's a misconception that the President can issue an "executive order" that overrules Congress. Such an order would have no force, and would fail in front of a federal court --- you saw this with the original Trump Muslim Ban.
It is quite typical for many countries and Belarus is definitely not the worst one in this sense. For example, the situation in Latvia and Estonia is much worse because everything is ok and fair but only until you have "right" ethnic origin (citizen of 1st class) - otherwise, if you do not belong to the titular nation then you are in trouble - the whole system will play against you.
No, not really. Especially not if you are conducting business.
But the moment your case is perceived by authorities as political or somebody with power finds your business interesting, one gets BIG troubles. Now, by playing by the rules one can protect somewhat from the "business" interests, so the situation is better than, for example, in Russia. But political part is very unpredictable and it is impossible to know which action can cross the line.