After having a little problem with Magento in several projects, we decided to put the functionality into a Magento module and share it with the other users. In Magento every product has a fixed attribute set that defines which attributes every product has. Unfortunately the attribute set cannot be changed after the product’s creation. This is in many productive contexts not an acceptable limitation.
This module overrides the standard behaviour and makes it possible to change attribute sets although the item has already existed. Thus we did our part making Magento even more flexible. 
The extension can be reviewed and downloaded at http://www.magentocommerce.com/extension/706/change-attribute-set.
