This custom hook allows you to reward posts being published based on the category they are assigned. The hook will reward points when a post is published, so if a category is added after publishing, it will not payout. Goes into your child theme's functions.php file or custom plugin.

mycred-publish-content-cat-hook

/**
 * Register Custom Hook
 * @since 1.0
 * @version 1.0
 */
add_filter( 'mycred_setup_hooks', 'mycred_pro_register_publish_content_category_hook' );
function mycred_pro_register_publish_content_category_hook( $installed ) {

	$installed['publish_category_content'] = array(
		'title'       => __( '%plural% for Publishing Content (Categories)', 'mycred' ),
		'description' => __( 'Award users points based on the category a post is published in.', 'mycred' ),
		'callback'    => array( 'myCRED_Publish_Content_Category' )
	);

	return $installed;

}

/**
 * Load Custom Hook
 * @version 1.0
 */
add_action( 'mycred_load_hooks', 'mycred_pro_load_publish_content_category_hook' );
function mycred_pro_load_publish_content_category_hook() {

	class myCRED_Publish_Content_Category extends myCRED_Hook {

		public $categories = array();

		/**
		 * Construct
		 */
		function __construct( $hook_prefs, $type = MYCRED_DEFAULT_TYPE_KEY ) {

			$this->categories = get_categories( array( 'hide_empty' => false ) );

			$defaults         = array();
			foreach ( $this->categories as $cat )
				$defaults[ $cat->slug ] = array(
					'creds'     => 0,
					'log'       => '%plural% for publishing content',
					'limit'     => '0/x'
				);

			if ( isset( $hook_prefs['publish_category_content'] ) )
				$defaults = $hook_prefs['publish_category_content'];

			parent::__construct( array(
				'id'       => 'publish_category_content',
				'defaults' => $defaults
			), $hook_prefs, $type );

		}

		/**
		 * Run
		 * @version 1.0
		 */
		public function run() {

			add_action( 'transition_post_status', array( $this, 'maybe_publish' ), 10, 3 );
			add_filter( 'mycred_all_references',  array( $this, 'add_badge_support' ) );

		}

		/**
		 * Add Badge Support
		 * @version 1.0
		 */
		public function add_badge_support( $references ) {

			foreach ( $this->categories as $cat ) {

				$ref = 'published_' . $cat->slug;
				if ( ! array_key_exists( $ref, $references ) )
					$references[ $ref ] = sprintf( 'Published content in %s', $cat->name );

			}

			return $references;

		}

		/**
		 * Maybe Publish
		 * @version 1.0
		 */
		public function maybe_publish( $new_status, $old_status, $post ) {

			// Check for exclusions
			if ( $this->core->exclude_user( $post->post_author ) === true ) return;

			// We want to fire when content get published or when it gets privatly published
			$status         = apply_filters( 'mycred_publish_hook_old', array( 'new', 'auto-draft', 'draft', 'private', 'pending' ) );
			$publish_status = apply_filters( 'mycred_publish_hook_new', array( 'publish', 'private' ) );

			// Make sure this is the right transition
			if ( in_array( $old_status, $status ) && in_array( $new_status, $publish_status ) ) {

				// Get all the categories the post belongs to in case we have more than one
				$assigned_categories = get_the_category( $post->ID );

				// Loop through all assigned categories
				if ( ! empty( $assigned_categories ) ) {
					foreach ( $assigned_categories as $category ) {

						// If we set a vale of zero, skip
						if ( ! array_key_exists( $category->slug, $this->prefs ) || $this->prefs[ $category->slug ]['creds'] == 0 ) continue;

						// Add this under a custom reference
						$reference = 'published_' . $category->slug;
						$data      = array( 'ref_type' => 'post' );

						if ( ! $this->over_hook_limit( $category->slug, $reference, $post->post_author ) )
							$this->core->add_creds(
								$reference,
								$post->post_author,
								$this->prefs[ $category->slug ]['creds'],
								$this->prefs[ $category->slug ]['log'],
								$post->ID,
								$data,
								$this->mycred_type
							);

					}
				}

			}

		}

		/**
		 * Preference for Viewing Content Hook
		 * @version 1.0
		 */
		public function preferences() {

			foreach ( $this->categories as $cat ) {

				$prefs = shortcode_atts( array(
					'creds'     => 0,
					'log'       => '%plural% for publishing content',
					'limit'     => '0/x'
				), ( ( array_key_exists( $cat->slug, $this->prefs ) ) ? $this->prefs[ $cat->slug ] : array() ) );

?>
<div class="hook-instance">
	<h3><?php printf( 'Published in: %s', $cat->name ); ?></h3>
	<div class="row">
		<div class="col-lg-2 col-md-6 col-sm-12 col-xs-12">
			<div class="form-group">
				<label for="<?php echo $this->field_id( array( $cat->slug => 'creds' ) ); ?>"><?php _e( 'Amount', 'mycred' ); ?></label>
				<input type="text" name="<?php echo $this->field_name( array( $cat->slug => 'creds' ) ); ?>" id="<?php echo $this->field_id( array( $cat->slug => 'creds' ) ); ?>" value="<?php echo $this->core->number( $prefs['creds'] ); ?>" class="form-control" />
			</div>
		</div>
		<div class="col-lg-4 col-md-6 col-sm-12 col-xs-12">
			<div class="form-group">
				<label for="<?php echo $this->field_id( array( $cat->slug, 'limit' ) ); ?>"><?php _e( 'Limit', 'mycred' ); ?></label>
				<?php echo $this->hook_limit_setting( $this->field_name( array( $cat->slug, 'limit' ) ), $this->field_id( array( $cat->slug, 'limit' ) ), $prefs['limit'] ); ?>
			</div>
		</div>
		<div class="col-lg-6 col-md-12 col-sm-12 col-xs-12">
			<div class="form-group">
				<label for="<?php echo $this->field_id( array( $cat->slug => 'log' ) ); ?>"><?php _e( 'Log Template', 'mycred' ); ?></label>
				<input type="text" name="<?php echo $this->field_name( array( $cat->slug => 'log' ) ); ?>" id="<?php echo $this->field_id( array( $cat->slug => 'log' ) ); ?>" placeholder="<?php _e( 'required', 'mycred' ); ?>" value="<?php echo esc_attr( $prefs['log'] ); ?>" class="form-control" />
				<span class="description"><?php echo $this->available_template_tags( array( 'general', 'post' ) ); ?></span>
			</div>
		</div>
	</div>
</div>
<?php

			}

		}

		/**
		 * Sanitise Preferences
		 * @version 1.1
		 */
		public function sanitise_preferences( $data ) {

			foreach ( $this->categories as $category ) {

				if ( isset( $data[ $category->slug ]['limit'] ) && isset( $data[ $category->slug ]['limit_by'] ) ) {
					$limit = sanitize_text_field( $data[ $category->slug ]['limit'] );
					if ( $limit == '' ) $limit = 0;
					$data[ $category->slug ]['limit'] = $limit . '/' . $data[ $category->slug ]['limit_by'];
					unset( $data[ $category->slug ]['limit_by'] );
				}

			}

			return $data;

		}

	}

}