Is it possible to set default values to attributes of work items from
certain types?

We currently do not provide a way to configure default values on a
per-attribute basis. The default values depend on the attribute type.

Exceptions are:

a) Enumeration attributes like priority and severity (and custom
enumeration). You can define their default value in the Process
Configuration.

b) State/Resolution: The workflows allow to define an initial state.

I have created Enhancement
https://jazz.net/jazz/resource/itemName/com.ibm.team.workitem.WorkItem/58629
that requests configurable default values on a per-attribute basis.

Patrick,
Jazz Work Item Team