Working a little more on this, I can now get the Annotation Scale (previously set to 2.0) of the model to apply to the text item:
ITextPartIdPtr textPart;
TextBlockPtr textBlock = textQueryHandler->GetTextPart(eehText, *textPart);
TextBlockPtr newTextBlock=textBlock->Clone();
DPoint2dCR scale = { 0.5, 0.5 };
newTextBlock->GetRunPropertiesForAddR().ApplyScale(scale, false);
eehText.Invalidate();
if (TEXTBLOCK_TO_ELEMENT_RESULT_Success != TextHandlerBase::CreateElement(eehText, nullptr, *newTextBlock))
printf("Text creation error\n");
IAnnotationHandler *annoHandler = dynamic_cast<IAnnotationHandler*>(&eehText.GetHandler());
StatusInt iStatus = annoHandler->AddAnnotationScale(eehText, ACTIVEMODEL);
but ApplyScale() doesn't seem to be doing anything...The text item gets an Annotation Scale of 2 applied to it, but the text is NOT reduced in size by 2.0, so instead of the text now displaying the same size (as before the modification), it is twice as large.
Bruce