I want to make the editor experience better and more visually pleasing when filling in content on a page (In all properties view). Could be a simple divider or a heading..
I am already using tabs, whenever it makes sense. Also, I have been experimenting with using blocks as properties. This adds a nice separation with at clear heading, but it is so much more code to maintain and a bit of a mess to be honest when the properties truly belong to the page type.
Out-of-the-box, it is not possible to decorate properties with headlines, unless you use block-properties, as you mention yourself.
However, I thought your question was quite interesting, and I discovered that extending Episerver to accommodate this behavior is surprisingly easy. I have written an example solution, which you're free to use as you like: https://arlc.dk/grouping-properties-with-headlines-without-property-blocks.
If you dislike the solution, an alternative approach would be to introduce your own Property-type (Headline), and create a 1) a custom dojo-widget to simply display a headline, and 2) an EditorDescriptor to set the ClientEditingClass. Linus wrote an excellent blog post on this here: https://world.episerver.com/blogs/Linus-Ekstrom/Dates/2012/7/Creating-a-custom-editor-for-a-property/.
EDIT: I see, I have skipped too quickly over the overriding part.
You don't have to override any files by replacing them, and you won't have to extract Shell.zip (unless you're curious how Episerver has implemented their widgets). The part that overrides the specific component is define("epi/shell/form/Field". As long as your definition of this widget is loaded after shell, dojo will use your implementation, whenever something is requiring "epi/shell/form/Field". The thing that ensures your implementation is loaded after, is in module.config, under 'This injects our field-implementation [...]'.
The path ~/ClientResources/Scripts/Shell/Field/Field.js is simply the location I have chosen to put the overriden version of Field.js. You can put it wherever you like, as long as you update module.config accordingly, with the new path. It works like this: First, Episerver defines widget A. Then you define a widget with the same name, A. When anything tries to fetch A, it returns your implementation, rather than Episerver's.