If you try to update it without the person_id you’ll get a “record not found” error. This is undocumentated as far as I’ve seen.
To keep your theme code clean, you could put the code into a partial, so it’s easy to include in specific events without having to duplicate a bunch of code every time.
If you’re looking for general help on how to customize templates, I’d start here: https://nationbuilder.com/theme_documentation
Here’s NationBuilder’s guide on how to create a custom theme: https://nationbuilder.com/theme_documentation
Make sure you have Action applied to your site before you begin that process, so you can choose the option to “Clone your current theme (Action)”.
Once you’ve created the custom theme, you can edit the values in the file _homepage_excerpt.html. Each page type is labeled in the file, for example "" is at the top of the code for the Volunteer Signup page homepage widget. You’ll then find the call-to-action text below that, which you can change. Then save and publish the theme, and switch your site over to your new custom version of Action!
I hope that helps,