Hi Gretchen, that’s not really a plugin question, but for WordPress itself. Looking at the code to manage the RSS feed, it looks like you could probably change the value of the RSS feed type option during the feed output. Something along the lines of this for a start, maybe:

add_filter( 'option_rss_use_excerpt', 'prefix_maybe_modify_rss_feed' );
/**
 * Maybe change the RSS feed output based on the post type.
 *
 * @param bool $option
 * @return bool
 */
function prefix_maybe_modify_rss_feed( $option ) {
	$post_type = get_post_type();
	if ( 'different_post_type' === $post_type ) {
		// return a different value
	}

	return $option;
}

You’d need to experiment with how to change it based on the base site setting and what you want to change, but I think that should be a start.