The short Microsoft answer is that starting Office 2007 there is no way to update the XSD Schema you imported and the only option is to Import the updated one, remove the previous and rebind tables. (takes long time)
I though to my self why is it too hard to implement ?
So for my test i created two Schema (old and new) :
The only difference is that i added two attributes.
I created two excel sheets (and binded to relevant schema)
I renamed the two XLSX files to ZIP and compare its content :) (I could have used OpenXML also)
While comparing the two files, I saw that there is specific XML file that interest me called “xmlMaps.xml”
And when i compare its content than i saw the solution:
So at the end the XSD is imported as regular text, and you can “update” it by updating the xmlMaps.xml (update your specific XSD and not others)
My next small project is to create tool to refresh Schema :)