Thanks for the clarifications!
As an aside, I just noticed that some terminology - import/copy and project/template -was used inconsistently though I have no idea if that is important. (reference the emphasis above)
The first example is interchangeable. With style import (or copying styles from one project into another, if you will), you must target an existing project to import from. Project templates are not projects yet, so they cannot be targetted.
Templates, at least by default, do not store styles and will use your application defaults to create the new project with. It is possible, when creating a new project template, to save the styles used in that project instead of your defaults.
Thus, creating a project from a template, modifying the styles in that project, and then using it to save a template (potentially overwriting the previous template if it is custom), with that checkbox enabled to store styles, will update the template. That’s the only way to get style changes into a template.
If I didn’t misunderstand, and I opt to import/copy all the styles into a (new empty and blank) project/template, couldn’t I then edit or delete all these imported/copied styles as I choose?
Of course! Once you import styles into a project, they are entirely editable, and frankly no different than any other styles you’ve made in that project (or the defaults that are created for you). You can revise them, delete them, etc.
If so, in theory, now I have a (new empty and blank) project or template that only contains the “certain styles” that I wanted plus the updated version of another.
Yup! Though it is worth mentioning that if styles are your only reason for making a custom blank project, that is an unnecessary step. You can override the application defaults with the current project’s stylesheet in File ▸ Options...
, under Editing: Formatting. You’ll find a Set Styles Defaults...
button at the bottom. Don’t worry, you can reset to factory defaults with this same button if you end up preferring to keep those for most new projects.
That said, having your own blank starter is a very useful thing for any of the small little settings you prefer. For example I can’t use Scrivenings mode without the option to show item titles in the text, and I like having labels colour all the icons. Stuff like that, project settings, are all saved into templates, including whatever labels you prefer, custom metadata fields, etc. Think of personal project templates as a second layer of settings you can make use of.