Find/replace key-value pairs

Hi all:

I have an OmniGraffle document with quite a number of objects on it that 
use key-value pairs as metadata. One key is called "cite". I'd like to 
replace all occurrences of the key-value pair key:"cite" - value:"abc" 
with key:"cite" - value:"def". All other key-value pairs should stay as 
they are. Is there an easy way to do this?

In other words: How can I select all objects that have the key-value 
pair key:"cite" - value:"abc"?

(I could save the document in plain text and use my text editor, but 
maybe there is a way do do this from within OmniGraffle.)

Cheers,
Claus