Na na na na Na na na na BBATMAN!

Need a handy tool for editing attributes within all blocks at the same time? AutoCAD has a great tool built right in - BATTMAN

You can get at all the defined blocks in the drawing that have attributes, and you can get at all the atts within a block. You can change all kinds of things about those atts as well.

PS - This can also be found on the Modify menu: Object » Attribute » Block Attribute Manager and the Modify II toolbar