[WooCommerce Subscriptions]Disallow downgrading for "WooCommerce Subscriptions" Grouped Product-Subscriptions

functions.php

<?php

// Prevent Downgrading
add_filter( 'woocommerce_subscriptions_switch_is_identical_product', function( $is_identical_product, $product_id, $quantity, $variation_id, $subscription, $item )
{

	if ( wc_get_product( (int) $product_id )->get_price() < $item->get_product()->get_price() )
	{

		$is_identical_product = true;

		add_filter( 'woocommerce_subscriptions_switch_error_message', function()
		{

			return 'Downgrades are not possible.';

		});

	} // end if

	return $is_identical_product;

}, 10, 6 );

// Remove Subscription update button if current subscription id matches an array-item
add_action( 'woocommerce_order_item_meta_start', function( $item_id, $item, $subscription )
{

	if ( in_array( $item->get_product()->get_id(), [ 204361 ] ) )
		remove_action( 'woocommerce_order_item_meta_end', [ 'WC_Subscriptions_Switcher', 'print_switch_link' ] );

}, 10, 3 );

Does this work with variable products subscriptions?

Yes, works fine for variable subsciptions also

Unfortunately this code doesn't work, you can add the product to your shopping cart (although it says it's not possible) and order it :(