default_rating_form_by_category.php

<?php
/**
 * Sets default rating form for a post based on category
 * 
 * @param int $rating_form_id
 * @param int $post_id
 * @param array $params
 * @return $rating_form_id
 */
function mrp_default_rating_form_by_category( $rating_form_id, $post_id, $params ) {

	if ( $post_id ) {

		$terms = get_the_terms( $post_id, 'category');
		
		if ( $terms && is_array( $terms ) ) {
			
			if ( in_array( 'category1', $terms ) ) {
				$rating_form_id = 1;
			} else if ( in_array( 'category2', $terms ) ) {
				$rating_form_id = 2;
			}
		}
		
	}

	return $rating_form_id;
}
add_filter( 'mrp_default_rating_form', 'mrp_default_rating_form_by_category', 10, 3 );