Add new option to Genesis Content Archives display dropdown, and amend the toggles config to also show the Limit setting if the new value is chosen. Requires Genesis 1.8.0 to work, since neither filter existed until then.

gistfile1.aw

<?php

add_filter( 'genesis_archive_display_options', 'child_add_content_archive_display_option' );
/**
 * Adds new option to display type in Genesis Theme Settings Content Archives
 * box.
 *
 * @param  array $options Existing display types.
 * @return array          Amended display types.
 */
function child_add_content_archive_display_option( array $options ) {

	$options['contentplus'] = __( 'Display 1 full post then limited content', 'child-domain' );
	return $options;

}

add_filter( 'genesis_toggles', 'child_amend_toggles' );
/**
 * Filter one value in the existing list of Genesis toggle settings.
 *
 * Works by casting the check_value from a string to an array, and merging the new
 * value with the old one(s). This allows other plugins or theme code to play nicely too.
 *
 * @param  array $toggles Existing array of toggle settings.
 * @return array          Amended toggle settings.
 */
function child_amend_toggles( array $toggles ) {
	
	$toggles['content_archive'][2] = array_merge( (array) $toggles['content_archive'][2], array( 'contentplus' ) );
	return $toggles;
	
}