You can link the text within the balloon to Iproperties. I am assuming you want to link it to the "Part number" iproperty?
click to create a balloon
when prompted under 'BOM view' select 'Parts only'
Right click on the balloon and select edit 'balloon style'
under 'Property display' click on the button 'property chooser'
now add the iproperties you want.
The text in the balloon will update when linked in this way.
You can save these settings in your template so it is ready to go
