Create a new rule Go into the properties and under Content Types, click on the types you want to block. If you are going to edit the extentions, 1st copy them into a new content type and edit that content type. Unless you need to, be sure to remove .js extension or just about every page will have an error. Add the groups that you want it to apply to and apply the changes.
I'm not sure if you can add the actual file name in here or just the TYPE of files. It would be a lot easier to filter out all executable content to all users and create another rule that allows downloads from specific sites or you will need to keep your eyes on the logs daily to see what they are d/ling.