How to append text to set of RTF records

One part of my workflow is taking notes on books. At the end of my process, I have a folder full of rich text notes for the book. I’d like to add some source metadata, as text, to each file.

Is there a way to use a script to automatically append the same chunk of text to a selection of records?

As a concrete example, one initial record might be:

I’d want to add the author and book source info so it never gets separated from the notes. So, the final version of that record would become:

Have you considered adding these as Tags?

From where are you getting the info ?
Are you typing it in?

A simple example of inserting some text in the currently displayed RTF file is…

property enteredText : ""
-- This values is cached and reused when the script is run again. However, the value does NOT persist between launches of DEVONthink.

tell application id "DNtp"
	if type of content record is rtf then
		set enteredText to text returned of (display dialog "Enter the copy to be inserted." default answer enteredText)
		tell text of think window 1
			make new paragraph at end with properties {text:return & enteredText}
		end tell
	end if
end tell