jetpack_cdn_plugin_slug_and_versionFilters Jetpack CDN’s plugin slug and version number. Can be used to override the values that Jetpack uses to retrieve assets. For example, when testing a development version of Jetpack the assets are not yet published, so you may need to override the version value to either trunk, or the latest available version. Expects the values to be returned in an array.
jetpack_cdn_core_version_and_localeFilters Jetpack CDN’s Core version number and locale. Can be used to override the values that Jetpack uses to retrieve assets. Expects the values to be returned in an array.
jetpack_lazy_images_skip_image_with_attributesAllow plugins and themes to conditionally skip processing an image via its attributes.
jetpack_contact_form_input_classFilters the “class” attribute of the contact form input
jetpack_contact_form_submit_button_classFilter the contact form submit button class attribute.
grunion_contact_form_delete_feedback_postFilters whether to erase a particular Feedback post.
jetpack_should_use_minified_assetsFilters the switch that if set to true allows Jetpack to use minified assets. Defaults to true if the SCRIPT_DEBUG constant is not set or set to false. The filter overrides it.
jetpack_postimages_ignore_minimum_dimensionsFilters the switch to ignore minimum image size requirements. Can be used to add custom logic to image dimensions, like only enforcing one of the dimensions, or disabling it entirely.
jetpack_updated_themesSignals to the sync listener that one or more themes was updated and a sync action reflecting the update and the theme info should be sent
Jetpack Developer Resources 