Fine-tuning "Open safe files after downloading"

Solution 1:

The preferences file is located at ~/Library/Preferences/com.apple.DownloadAssessment.plist

If the file doesn't exist, then create it and include the following:

<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com-PropertyList-1.0.dtd"> 
<plist version="1.0"> 
    <dict> 
        <key>LSRiskCategorySafe</key> 
        <dict> 
            <key>LSRiskCategoryExtensions</key> 
            <array> 
                <string>docx</string> 
                <string>xlsx</string> 
            </array> 
        </dict> 
    </dict> 
</plist>

To exclude Zip files, add the following to the preferences:

<dict> 
    <key>LSRiskCategoryNeutral</key> 
    <dict> 
        <key>LSRiskCategoryExtensions</key> 
        <array> 
            <string>zip</string> 
        </array> 
    </dict> 
</dict>

More info at: Source