Can the customers change the products in their subscription?

Yes, customers can remove and add new products to their subscriptions. You can turn on this functionality in Seal Subscriptions -> General Settings -> Customer portal -> Allow customers to add/remove products from the subscription. 

Your customers can also change their email address, edit their shipping info, change the subscription interval, change the quantity of the products, skip future orders in the subscription and of course pause, resume, cancel and reactivate their subscription. You have total control over what you allow your customers to edit in their subscription. 

Shop owners can also add or remove products from the subscription in the app itself. You can edit a specific subscription by going to your App settings -> Subscriptions -> click on a subscription -> Edit subscription. This functionality allows you to edit every part of the subscription, including product prices.