As per the API documentation:

SLASettings

Related Settings for Service Level Agreements setting of the site. Allowed values: copy (Copy Default Settings ), refer(Refer Default Settings ), custom(Custom Settings)

What is the appropriate usage of this as it is not clear. How do I actually set custom settings, an example would help! If I have two SLAs in the default settings called "Premium SLA" and "Standard SLA" how would I set that using the API for the site?