The original sentence is fine. "Prepared" is being used as an adjective there. It means a text that had been prepared.
Student or Learner
I have a question about the usage of the verb "follow". According to dictionaries, "follow" means "act in accordance with". So, "follow" should be used with something that indicates what do to (expected action) , like "plan" and "agreement". But, I found this on google:
"But rather than follow the prepared text written by Cody Keenan, the chief White House speech writer, Obama showed the Republican Congress his sassy side with an ad-lib."
"Prepare text" does not indicate what to do. Rather, "prepare text" indicates what to say. So, "follow the prepared text" seems weird. Would the following rewrite:
"But rather than follow the act of giving a speech of the prepared text written by Cody Keenan..."
, be better?