Here is a Nietzschean perspective, from Heidegger, Off the Beaten Track (pages 170-171 & 184)
The essence of value is based on its being a viewpoint. Value means
that which one has in mind [ins Auge gefasst]. Value is the point of
sight for a seeing that has its eye on something, or, as we say, that
counts on [auf etwas rechnet] something and thereby ...
You are correct that the CI does not mandate any specific code of behavior. The CI says:
Act only according to that maxim whereby you can, at the same time, will that it should become a universal law.
But what is a "maxim"? If we allow any rule of behavior as a maxim, then a person named Dave Jackson could say, "steal if your name is Dave ...