If we are talking about resizing text on a CAD annotation layer, it can be done. But the changes to the font are not always obeyed. Sometimes the font will change, other times it will not. The image of the dialog below shows where the font controls are.
Could this be related?
http://support.esri.com/en/bugs/nimbus/TklNMDEwOTI0
This issue has been around in ArcMap as long as I can remember.
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