<Update> doesnt like <ExtendedData>

[gofootn]

I am trying to do a dynamic update via a NetworkLinkControl

I have an <Update> <Change> set of tags. It works fine for updating
<name> or <Point> inside a placemark

If i include <ExtendedData> in the update, I get an error:

cannot modify array element

I saw an unanswered post that suggested putting an id/targetId on the
ExtendedData tag. If I do this I get an error:

Cannot nest <targetId> (my id)

How do you update the ExtendedData when it has changed? I cant find a
specification that indicates what can be modified inside of a Change
tag. Is there such a definition?

thanks
Rich