The SoftLayer API provides direct control over every aspect of SoftLayer services, as well as your SoftLayer customer account.
It means that support for Domains and Billing information is available.
Regarding updating prices and setting up your own graphic design is a job that should be done by yourself.
These are some links that could help you with your requirements.
http://sldn.softlayer.com/
http://sldn.softlayer.com/reference/services/SoftLayer_Dns_Domain
Nevertheless, you could submit a ticket to SoftLayer, so that they might provide you further assistance.