Look on your AFM and MX books and see if it covers "operations with mixed engines".
Do not know what for the 737.
In the 747, we can mix different dash number engines.
Requires reduction of performance data, and labels on engine instruments.
Was same story with the JT8D-7 and -9, or -11, -15, and -17 in the 727s.
Basically requires reduced T/O EPR to the EPR of lowest "dash"
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Happy contrails