I see.
So it can be left to subjective whims then, as long as they follow what is written in the Cathechism.
Which seems to me, wide as the Grand Canyon, no?
Exactly. Except that it is not the Catechism which is the guide. In fact no one seems to be quite sure what is the guide, which in effect makes their leeway even wider than the grand canyon. There was the old GIRM which is being replaced by a new GIRM. But neither one really specifies the "fundamental norms" outside of which the adaptations required of the bishops are not supposed to stray.