Can I run the same Job definition at the beginning and end of the jcl WITH A DIFFERENT FILE DEFINITION then retrieve stored count from the first JOB definition?
First Run Job Def Name: TES001DPUARTOTAL
File definition: Tally all records in File
Internal Item: (I-001) Tally count
History Item: (E-001) Retrieve external job results
Rule: (R-001) [ I-001 EQ E-001]
Second run job Def Name: TES001DPUARTOTAL
File Definition: Embedded Key: Messages Written
Internal Item: (I-???) Messages Written
History Item: (E-???) Retrieve First Job (I-001) results stored in DB
Rule: (R-???) - [ I-??? EQ E-001 ]
What you mention should be possible, though the JCL would need to be tested to ensure it has been built properly. If any issues surface in your testing feel free to open a support ticket.