A subtopic came up as a Report issue where the solution was to use the Style Editor.
While reviewing the possibilities, it occurred to me that @ztlxltl was doing something similar in the Configuration options for the experimental FamilyTreeView. But parts of his approach were more intuitive.
Specifically, when trying to make a modification to a hard-coded style, he automatically creates a “(copy)” and switches focus to it. Meanwhile, in the Style Editor, the Edit and Delete buttons are nonfunctional if the selected style is hard-coded or no style is selected, but the buttons are not ‘dimmed’. So the feature appears to be broken. (I remain uncertain if the Add button is a copy of the default style or is based on something else.)
On the other hand, complex addons like FamilyTreeView by @ztlxltl and CardView by @cdhorn have MASSIVE configuration dialogs that create an undue burden on Translators. And it seems like the Style Editor has the potential to reduce duplication of code and translation burden.