Is it possible to attach SLAs to a ticket using Service Desk SOAP Web Services?
Service Desk 17.1 or previous versions
Out of the box there is no method that can be used to attach SLAs to tickets. It is not recommend the usage of the update object method since this activity require not only one object of the schema and therefore it is risky and it could lead to missing data. You might use a different approach by attaching a service type to another variable of the ticket like a category which can attach a service type in case that is modified. The additional suggestion is to contact CA Services if this is going to a requirement for your company and create/vote the idea in the Service Management community.