Am trying to establish a default or startup template so that when I try to create a blank document in InDesign CS4, it has the page layout, styles, and swatches that I want to use. I thought the place to store this would be (am running Windows 7 Professional Service Pack 1) C:\Program Files (x86)\Common Files\Adobe\Templates\en_US\InDesign\6.0\blank.indt
But when I change elements of this template, new blank documents that I create in InDesign don't change with it.
That's not how it works. A template needs to be opened to set all the parameters for the document.
You'll see if you open it the file will be called untitled-1.indd.
How did you try to modify the blank template? You need to describe the entire process (and I'm not sure that messing with that template is really a good idea -- why not create a custom template and just open it?).