Is there a way to modify keychain item ACL descriptions?
After quite a tedious research it seems that there is no easy way to edit the description of the private key, so basically unless Apple enhances their Keychain Access application there is no way to distinguish between multiple digital IDs imported into the same key chain.

It also looks like Google Chrome (and Chromium) have implemented some key management routines and are managing the descriptions of imported private keys.  However, I didn't figure out exactly how to leverage this functionality yet.

Anyway, the short answer to my question: there is no way to modify item's ACL and/or their descriptions in OS X keychain at the moment and it seems that nobody really cares.