Snippet to switch UPS Account Based on Shipping Class. WooCommerce UPS Shipping Plugin with Print Label - https://www.pluginhive.com/product/woocommerce-ups-shipping-plugin-with-print-label/

functions.php

/**
 * Snippet to switch UPS Account Based on Shipping Class
 * Created at : 16 December 2020
 * PluginHive Plugins : Switch UPS Account Based on Shipping Class
 * Gist Link : https://gist.github.com/PluginHive/a7cf9e022e34dc71c5f678d3bf7cb147
**/

add_filter( 'wf_ups_shipment_settings', 'ph_ups_modify_settings_datas', 10, 2 );

function ph_ups_modify_settings_datas( $settings, $order ) {

	// Add Alternative Accounts
	$alternate_accounts = array(
		// Shipping Class to use Alternative Account
		'class-a' => array(
			//Alternative Account Details
			'shipper_number'		=> 'XXXXX', 		// UPS account number
			'user_id'			=> 'XXXXXXXXX', 	// UPS user ID
			'password'			=> 'XXXXXXXXXXX', 	// UPS password
			'access_key'			=> 'XXXXXXXXXXXXXX', 	// UPS access key
			'origin_addressline'		=> '420 9th Ave', 	// Origin address
			'origin_postcode'		=> '10001', 		// Origin postcode
			'origin_city'			=> 'New York', 		// Origin City
			'origin_state'			=> 'NY', 		// Origin State
			'origin_country'		=> 'US', 		// Origin Country
		),
		// Shipping Class to use Alternative Account
		'class-b' => array(
			//Alternative Account Details
			'shipper_number'		=> '111111', 		// UPS account number
			'user_id'			=> '11111111', 		// UPS user ID
			'password'			=> '1111111111', 	// UPS password
			'access_key'			=> '111111111111', 	// UPS access key
			'origin_addressline'		=> '200 exp Ave', 	// Origin address
			'origin_postcode'		=> '11354', 		// Origin postcode
			'origin_city'			=> 'Queens', 		// Origin City
			'origin_state'			=> 'NY', 		// Origin State
			'origin_country'		=> 'US', 		// Origin Country
		),
	);

	global $woocommerce;

	if( !is_cart() && !is_checkout() && empty($order) ) {
		return $settings;
	}

	$is_all_items_belog_shipping_class 	= false;
	$selectedShippingClass				= '';

	foreach ($alternate_accounts as $shipping_class => $alternate_account) {

		$is_all_items_belog_shipping_class = ph_is_all_items_belong_shipping_class($shipping_class, $order);

		if ( $is_all_items_belog_shipping_class ) {
			$selectedShippingClass = $shipping_class;
			break;
		}
	}

	if( !$is_all_items_belog_shipping_class ) {
		return $settings;
	}

	if ( !empty($selectedShippingClass) ) {

		$settings['shipper_number'] 		= $alternate_accounts[$selectedShippingClass]['shipper_number'];
		$settings['user_id'] 			= $alternate_accounts[$selectedShippingClass]['user_id'];
		$settings['password'] 			= $alternate_accounts[$selectedShippingClass]['password'];
		$settings['access_key'] 		= $alternate_accounts[$selectedShippingClass]['access_key'];
		$settings['origin_addressline'] 	= $alternate_accounts[$selectedShippingClass]['origin_addressline'];
		$settings['origin_postcode'] 		= $alternate_accounts[$selectedShippingClass]['origin_postcode'];
		$settings['origin_city'] 		= $alternate_accounts[$selectedShippingClass]['origin_city'];
		$settings['origin_custom_state'] 	= $alternate_accounts[$selectedShippingClass]['origin_state'];
		$settings['origin_country'] 		= $alternate_accounts[$selectedShippingClass]['origin_country'];
		$settings['origin_country_state'] 	= $settings['origin_country'].':'.$settings['origin_custom_state'];
	}

	return $settings;
}

function ph_is_all_items_belong_shipping_class( $shipping_class, $order='' ) {

	if ( !is_array( $shipping_class ) ) {
		$shipping_class = array( $shipping_class );
	}

	// For Label side
	if ( !empty($order) ) {
		foreach ($order->get_items() as $key => $item) {

			$product = $item->get_product();

			if ( in_array( $product->get_shipping_class(), $shipping_class ) ) {
				return true;
			}
		}

	//For Rate
	}else{
		
		global $woocommerce;

		foreach(WC()->cart->cart_contents as $key => $values) {
			if ( in_array( $values['data']->get_shipping_class(), $shipping_class ) ) {
				return true;
			}
		}
	}
	
	return false;
}