osx Create association with new/custom file types via Info.plist


Example

<key>CFBundleDocumentTypes</key>
<array>
    <dict>
        <key>CFBundleTypeIconFile</key>
        <string>Icon file for associated file</string>
        <key>CFBundleTypeName</key>
        <string>My file format</string>
        <key>CFBundleTypeRole</key>
        <string>Viewer</string> <!-- The value can be Editor, Viewer, Shell, or None. This key is required.  -->
        <key>LSItemContentTypes</key>
        <array>
            <string>UTI of the file</string> <!-- Existing UTI or create a UTI for your new file type -->
        </array>
        <key>LSHandlerRank</key>
        <string>Owner</string>
    </dict>
</array>

source