There was no need to create a separate thread for this. You could have asked in the "round table" or "forum" section.
You can check if everything worked by pressing the English button I or simply going to the scenario information. After the words "teamplate was," the name of the template is written.

"Is there a difference if the extension is specified in the Data section of the rmg.txt file or if it should be left as rmg without specifying the extension?"
If your system has file extension display enabled, it should be rmg.txt.