Yes you have the correct file.
However, what you likely want to be change is is not the hidden/not hidden property but rather whether it is shown in the [Quick] Styles Gallery. This is a checkbox on the Modify Style dialog.


Also, it is generally safer to make such modifications from within a blank document and save them to the templates rather than opening the Normal Template itself. While I open and change the normal template regularly, I hesitate to recommend it to anyone else because of the problems that can arise from improper editing of that template.