Exclude/change attributtes for billing/shipping fields on the WooCommerce checkout page

gistfile1.php

add_action( 'wp', 'uni_checkout_under_certain_circumstances' );

function uni_checkout_under_certain_circumstances() {
		if ( function_exists( 'is_checkout' ) && ( is_checkout() || is_ajax() ) ) {
			remove_action( 'woocommerce_before_checkout_form', 'woocommerce_checkout_coupon_form', 10 );
            // the following line disables "notes" field
			add_filter( 'woocommerce_enable_order_notes_field', '__return_false' );
            // an example of unsetting checkout fields
			add_filter( 'woocommerce_checkout_fields', 'uni_unset_billing_checkout_fields', 10, 1 );
            // an example of modifying atributtes of checkout fields
			add_filter( 'woocommerce_checkout_fields', 'uni_set_required_shipping_checkout_fields', 10, 1 );
		}
}

//
function uni_unset_billing_checkout_fields( $fields ) {
		$billing_keys = array(
			'billing_company',
			'billing_phone',
			'billing_address_1',
			'billing_address_2',
			'billing_city',
			'billing_postcode',
			'billing_country',
			'billing_state',
		);

		foreach ( $billing_keys as $key ) {
			unset( $fields['billing'][ $key ] );
		}

		return $fields;
}

//
function uni_set_required_shipping_checkout_fields( $fields ) {
		$shipping_keys = array(
			'shipping_phone',
			'shipping_address_1',
			'shipping_city',
			'shipping_postcode',
			'shipping_country',
			'shipping_state',
		);

		foreach ( $shipping_keys as $key ) {
			$fields['shipping'][ $key ]['required'] = true;
		}

		return $fields;
}