C4C marketing permission integration

Dear experts

I have a question regarding Marketing Permission of a customer.

I am trying to update the marketing permission code ( Customer.MarketingPermission.MarketingPermissionCode) of a customer, but the problem is that I need to specify which channel I would like to modify the permission ( for example: I want to update the permission to “Opt-in” of the channel “Phone”).

How can I Specify to which channel I want to modified the permission code??

My code looks like:

// the variable customer is the Customer retrieved via Query.

customer.MarketingPermission.MarketingPermissionCode = this.PermissionCode;

// the problem is that how I specified that I need to change that permission code to a specific channel (FAX. INT, TEL).

Thanks for your help.