I’m afraid this is not possible now. I’ll pass it to the plugin author and hope he can add it in the future updates.
If you need it now, you can always modify the core file and change how ACF saves the name. You can find the export() function in “wp-content/plugins/advanced-custom-fields-pro/admin/settings-tools.php”. Keep in mind that your changes will be overridden when you updated the plugin.
Hope this helps 🙂
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