I am assuming you are talking about "attached balloons", like this:
As far as I know, this is not supported by ETO. But you can change the numbers in the attached balloons using the Inventor API. The key thing -- apparently -- is that the so-called "attached balloons" are represented by an API object called "BalloonValueSets". Each attached balloon is an instance of "BalloonValueSet" (singular) within the "BalloonValueSets" (plural) collection. To create attached balloons, you use BalloonValueSets.Add. You can use the properties of "BalloonValueSet" to change the number/text displayed in a particular attached balloon.
Hope this helps.
Jon Balgley Autodesk Configurator 360 / Inventor ETO team Autodesk, Inc.