HYPALLAGE: He nodded his agreeing head

HYPALLAGE: a figure of speech in which the usual relations of words/phrases are interchanged, e.g. "He nodded his agreeing head."

Microsoft® Encarta® 2009. © 1993-2008 Microsoft Corporation

What such interchange is shown in the example He nodded his agreeing head ?

“He nodded his head, agreeing.” is not the same as "He nodded his agreeing head."

In “He nodded his head, agreeing”, agreeing is an adverb = in agreement.

In "He nodded his agreeing head", agreeing is an adjective modifying "head".

"He nodded his agreeing head" is not a good example of hypallage as it means He nodded his head that was nodding in agreement. which is nonsense.

A good example of hypallage is "On the idle hill of summer/Sleepy with the flow of streams/Far I hear..." (A.E. Housman, A Shropshire Lad) — "Idle", although syntactically modifying "hill", semantically describes the narrator, not the hill. (see https://en.wikipedia.org/wiki/Hypallage).