Will I be able to change the email address for customers with access to the Customer Portal?
Yes, you can change your customer’s email address in Zoho Subscriptions.
If you’ve enabled the Customer Portal for that customer, then you will have to disable the portal for them and then change the email address. Once changed, you can send them a portal invitation again using the new email address. Your customer will have to create a new password to log back into the portal.