Eep. Eep. Eep.
Leaving aside the political realities that powerful nobles will sternly limit this authority, legally, the king may not have authority to do so. He may, in fact, be (theoretically) endowed solely with executive authority; it is his place to enforce the laws and ancient customs. Made life really interesting when the king wanted to not only codify but also rationalize the law. In real life it was sometimes glided over that a change was a change, presenting it as if it were just clarifying or reminding of something, and plentiful legal fictions were hammered together to somehow or other shoehorn new situations under old laws. Even when the king could, in fact, promulgate law, there could be real legal requirements. And consider "the law of the Medes and Persians which altereth not" where the king could issue a law -- and had to stick to it, whatever he thought of the results.
Which leads, in very short order, to info-dumping issues. When considering the reader who doesn't know all this -- who thinks that all monarchy are absolute, and all absolute monarch can rule by whim -- the question is how much you can put in to explain it to him. Especially if you're working on a short story and so have a limited scope for everything. And taking into consideration that some readers are so adamantly certain of the things they know that just ain't so that you will never put in enough info-dumping to convince them of it. . . .
sigh The burdens of a writer's life.
Updated: No more discussion of current politics, please. (I may, in fact, delete those comments that discuss it now if they encourage such discussion.)