The way the text files work is explained in this Knowledgebase article:
Modifying your Mailing List
Under the section: Modifying Text in Mailing List Messages
I would suggest reviewing that section for a more complete understanding.
But essentially, yes, you would just copy and replace the relevant files.
What this patch does, it it makes the templates more "generic" than they were before. Prior to this patch you would have had to modify the text files for each list. Now you simply have to modify them for a single list and copy them to the others if you wish to use the same set of templates for each list. (Obviously, since the files for each list are saved separately, you also have the option of using different templates for different lists as well.)