If I'm understanding the question correctly, you currently have a map with traffic counts (feature class) and amounts (as annotation). In another map, you want to use the same annotation feature class for the same feature class but update the value in the annotation feature class TextString to reflect truck count AND not impact the first map. Correct? If this is true, then no. Annotation is a feature class just like points/lines/polygons so when edits are made and saved, it's done. What you may want to consider is an annotation feature class for trucks and another for non-trucks.
