Mapping Center Answer:

Nothing that applies to either 9.2 or 9.3.  There are some discussion forum threads that you may find useful in reading--once logged in I searched for "Annotatation symbol substitution" and set my search options just for ArcGIS Desktop and results that were newer than 1 year. 

Generally speaking, the symbol substitution is most useful when you don't change the size of the text.

Changing scales usually requires a pretty significant change in annotation size, which may work in some cases--depending on the projection of the map and your annotation (from a practical perspective they should be the same; and from a quality perspective they had better be the same).  It would help if you included a screenshot or PDF of the initial scale and then what you want the anno to look like at the new scale.