How can a macro retrieve specific element attribute values from XML in a file?

I see no reliable way to document the source of a model that's been reverse engineered. 

At minimum the server instance and database used in the merge operation need to be stored in the model but I can neither retrieve them directly from the MergeModelObject nor specify them explicitly TO the MergeModelObject.  This leaves me with no reliable way to insure data in the model matches the values used in the merge operation without reading the .cmo file which I'm loathe to do using string operations.