Hi Dask,
We have done this in our 10.1 environment. What you need to do is to add a Boolean attribute for your yes/no option to the Promotion Request type (or a subtype of it) in the Type and Attribute Manager. After that the information can be queried with a bit of Java code in your Promotion Request Review and/or Promotion Request Approval workflow. Use the new LWC<sorry I forgot the name right now> method which can return all kinds of attributes including IBA's.
The *actionmodel.xml/*actions.xml stuff is for something different. It's generally used to add user action menu picks to the action menus and a few other places. They do not store values but allows users to trigger - yes you guessed it - actions. What you want here is an attribute.