Can customers change a bundle that's already in the cart?

Add the Bundle summary — cart block and point its Bundle page setting to the page that contains the builder. A supported bundle page or drop-in design can reopen the group with current quantities and gift selections through its Edit bundle link.

Updating removes the old group and adds the revised selection. If the replacement add fails, Cinch makes a best-effort attempt to restore the original group; Shopify does not provide a transactional replace operation.