Functionality now available on release of new sdk release (7.1.a ,March 2015)
Before this release, some specialized messages should be called to update some entity fields, methods like assign request or set state request.
However, from this release on it would be able to be done from the Update message.
Please see the below table to see what are the deprecated methods.
Deprecated message request Attribute to update
<entity>. OwnerId *
<entity>. StateCode *
*<entity> refers to any entity that provides this attribute.
Source of the information: