Open a Terminal window, and paste in the following, including the trailing quote character. (Note, you will need to head over to the original article to copy and paste the command properly):
What this does is create two small locked files with the same name as the installer and the temporary download filename, thus preventing macOS from downloading the installer into that location. There should be two locked files that look like this:
When and if the time comes to upgrade to High Sierra, simply throw these two files in the trash, then proceed with the upgrade.
Hat tip to Lloyd Chambers and MacPerformanceGuide for this trick!