Although having the feature of persistent settings in core is nice, it may take quite a while before it's actually accepted. WordPress 3.5 is still quite far away.
So let's augment the global $_REQUEST array instead.
add_action( 'load-edit.php', 'wpse34956_force_excerpt' ); function wpse34956_force_excerpt() { $_REQUEST['mode'] = 'excerpt'; } This will lock up modes, forcing excerpt mode all the time, so let's turn let the user decide but keep it persistent using the user's metadata:
add_action( 'load-edit.php', 'wpse34956_persistent_posts_list_mode' ); function wpse34956_persistent_posts_list_mode() { if ( isset( $_REQUEST['mode'] ) ) { // save the list mode update_user_meta( get_current_user_id(), 'posts_list_mode', $_REQUEST['mode'] ); return; } // retrieve the list mode if ( $mode = get_user_meta( get_current_user_id(), 'posts_list_mode', true ) ) $_REQUEST['mode'] = $mode; } You can further interpolate post_type into all by taking into account the $_GET['post_type'] variable when available.
add_action( 'load-edit.php', 'wpse34956_persistent_posts_list_mode' ); function wpse34956_persistent_posts_list_mode() { // take into account post types that support excerpts $post_type = isset( $_GET['post_type'] ) ? $_GET['post_type'] : ''; if ( $post_type && !post_type_supports( $post_type, 'excerpt' ) ) return; // don't care if ( isset( $_REQUEST['mode'] ) ) { // save the list mode update_user_meta( get_current_user_id(), 'posts_list_mode' . $post_type, $_REQUEST['mode'] ); return; } // retrieve the list mode if ( $mode = get_user_meta( get_current_user_id(), 'posts_list_mode' . $post_type, true ) ) $_REQUEST['mode'] = $mode; } Viola! Persistent list mode per post type per user, no hacks.