Yes, you can change the product and the variant for your customer.
To do this, you will need first to add the product they want, and then delete the existing product they do not want.
Step 1: From Ongoing --> click Subscriptions --> click Subscription # you want to manage
Step 2: In the Subscription product section, click Add Product
Step 3: In the Subscription product section, click Edit --> click Remove Product.
Select the product you want to remove and click "Yes, Remove this product."
Here you can remove a product for a customer
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