cloning and setPortletProperties

I've a question on invoking setPortletProperties on a POP.

I searched the spec, but could not find any reference to this question. 
I did find an assertion statemenet (AS109) which reads

"The properties of a cloned portlet may be set explicitly (via 
setProperties()) or opaquely (via "wsrp:edit" mode)."

[I just noted that the operation name needs to be corrected in this 
statement.]

So, my question is whether it is valid to invoke setPortletProperties on 
a POP? The spec says that POPs are not modifiable, but we don't 
explicitly define what cannot be modified.

Thanks

Subbu