The missing step is, if you change the property value, then you need to navigate to this location
~/Library/Application Support/DEVONthink Pro 2/Templates.noindex/Note.templatescriptd/Contents/Resources/en.lproj/Note.rtf
and also change the name of the “Note.rtf” document. This document is the “real” template and the script property has to be the same name – without the “.rtf” extension, of course.
Look further into the script and you will see this statement
set theTemplateFiles to helperLibrary's pathToLocalizedResources() & (((my helperLibrary's localizedString(pTemplateName)) & ".rtf") as string)
into which the code substitutes the value of “pTemplateName” and expects to find a document with that name. In your case, the script failed here.
In Finder, right-clicking or control-clicking any package (an .app, .templatescriptd, etc.) and choosing “Show Package Contents” will expose the folders inside the package for navigation and editing.