About Scrivener 1 script settings and Scrivener 3 styles

I have a screenplay written in Scrivener 1 that made extensive use of script settings. I find I now need to change some of these settings. I’m now using Scrivener 3.

Can I have some advice on the least painful way of doing this? For example, in Scrivener 3, can text in a script format also have a style? Can a script format be associated with a style, so that all the text in that script format could be updated? How are script formats and styles related?

It’s the same exact process as in Scrivener 2, not much as changed about how script settings are managed and updated in a project. The details of this panel and how to get to it are found in §19.6, Creating Your Own Script Formats, in the user manual PDF.

Even though most (if not all) modifications are reversible, given the nature of the process, there is no undo, so I advise making a backup before making changes.

Regarding your questions about styles, I would not try to mix the two together. It certainly is not designed to be used that way, and in fact that style related shortcuts all swap over to script related shortcuts (pop-up menu, numbered keys with Shift+Alt). That should be a hint they are meant to be mutually exclusive systems.