I am aware one can buy new character slots at in-game store or from NCSoft (9.99 USD if I remember well). This requires one's credit card, of course. Is there any other way of getting new character slots and attaching it to an existing account that does not require using credit card?
I have all 3 campaigns and EOTN on my account. I can buy a new campaign key for cash quite cheaply. Note I do not want to create new account, I just want to add characters to existing account and not to use a credit card. If I get another campaign key (say Nightfall one) and then use 'add access key' to my existing account that already has Nightfall - will it add 4 character slots? Or the new access key will work only for a new account as Nightfall already exists on the account?
thanks for resolving this mystery

Deadly