We looked at this exact setup recently but realised you can't suppress the unsubscribe link from any email customer.io sends.
You can set a flag so the user can't unsubscribe if you have a legitimate reason (e.g. transactional email) but I'm not a fan of the customer experience here as unsubscribe should mean that, unsubscribe.
You can set a flag so the user can't unsubscribe if you have a legitimate reason (e.g. transactional email) but I'm not a fan of the customer experience here as unsubscribe should mean that, unsubscribe.