Can I subsequently modify my payment method?

Yes. To change the payment method of your current order, log in to your customer account.
Should you not have your login details handy, please use our shop’s "Forgot your password" function. A link to create a new password will be sent within a few minutes to the e-mail address you specified when creating the customer account. 
After having logged in, please click on "My Orders" and then click on "View" next to the order which payment you want to modify.  
You can now select a new payment method and, depending on the chosen payment method, make the payment directly online.
If you have placed your order as a guest, please contact our customer service, who will make the modification for you.