Well, you could always just make all sets in dept A prime line to pool A and all sets in dept B to pool B.
However, on my MICS 5.0 I was able to assign a single digit, universal, external access code (under access codes in system programming, btw...available single digit external codes will vary from system to system depending on your existing numbering plan) and then by denying access to all line pools but one on the individual sets, I was able to dial 4 from one set and get pool A and 4 from another set and get pool B.
That should work on your system with 9 if you alter your numbering plan to free it up first.
If you are currently using 9 as a line pool code or in a routing table, that would prevent you from assigning 9 as the external access code.
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