jetpack_sync_unlock_sync_callableUsed to signal that the callables await transient should be cleared. Clearing the await transient is useful in cases where we need to sync values to WordPress.com sooner than the default wait time.
jetpack_nova_menu_item_loop_classFilter a menu Item Markup element’s class attribute.
jetpack_nova_menu_item_loop_close_elementFilter a menu item’s element closing tag.
jetpack_nova_menu_item_loop_open_elementFilter a menu item’s element opening tag.
jpp_allow_loginShort-circuit check_login_ability. If there is an alternate way to validate the current IP such as a hard-coded list of IP addresses, we can short-circuit the rest of the login ability checks and return true here.
jetpack_sso_auth_cookie_expirtationDetermines how long the auth cookie is valid for when a user logs in with SSO.
jetpack_seo_meta_tagsCan be used to edit the default SEO tools meta tags.
jetpack_seo_site_hostCan be used to insert custom site host that will used for meta title.
jetpack_seo_meta_tags_conflicted_themesCan be used to specify a list of themes that set their own meta tags. If current site is using one of the themes listed as conflicting, inserting Jetpack SEO meta tags will be prevented.
jetpack_seo_custom_titlesCan be used to prevent SEO tools from modifying site titles.
Jetpack Developer Resources 