Block Of Text I can Manage/Update Centrally For a Bunch of Posts

Hello,

I would like to add a section of text (header with couple paragraphs) in multiple blog posts. I would also like to be able to update the text from time to time. Is there a way to do this with a code block and some custom coding? I don't believe there is a native Squarespace feature that can perform this task.

All blog posts will use same text and you can adjust it from one location. You mean this?

Not really. I'm trying have a section of text (text block) that I can insert into multiple posts but manage the contents of that text block centrally. That way if I need to update the text, I don't have to go back to every post and re-update them all. 

I can't place this in the footer, because (1) it will show on every blog post and (2) I need it in the middle of the post.

Putting blocks in the footer to be used in other locations is a common technique to do what you want. You then use CSS to hide bits in the footer and then some CSS and/or JavaScript to move things into place.

Please see Blocks Boilerplate.

Let us know how it goes.