The full question

How can I make sure it's easy to come back and edit a Service Design Principle in the future?

My two cents: leave a Hemingway Bridge

As I'm writing on multiple drafts of my next Service Design Principles for the third volume in this series, I've started to write a little "Hemingway Bridge" note at the top. There I let my future self know what the simple things I could do to improve this text further are.

An example of a Hemingway Bridge I let myself in a note about this Service Design Principle.

It's an idea I borrow from Tiago Forte's book Building a Second Brain.

Here is a quote from the book:

"Besides his prolific works, Hemingway was known for a particular writing strategy, which I call the "Hemingway Bridge." He would always end a writing session only when he knew what came next in the story. Instead of exhausting every last idea and bit of energy, he would stop when the next plot point became clear. This meant that the next time he sat down to work on his story, he knew exactly where to start. He built himself a bridge to the next day, using today's energy and momentum to fuel tomorrow's writing."
You can also read more about this in the Google Books preview of the book.

If you are interested in building your own library of Service Design Principles, Tiago's book is definitely a good place to start.