“Is there a way to extend/add to the existing schema markup on posts and pages, so that one comprehensive schema output is generated?”
There are two ways:
- HTML Cards
- Post Code Injection (Use the Post Code Injection in the right Sidebar in the post or page you are editing and not the Main Code Injection).
I prefer the Post Code Injection.
I had a similar problem and Cathy helped me. You might wanna check this post out for further info:
What is the Best Way to Add FAQ Schema?
I hope this helps you.