Computer change no start no crank

The part number is exactly the same except for the last alpha character which according to the parts department guy at my local dealer only indicates the vendor of the part.
I could not locate an exact duplicate. I tried for 3 weeks.

The used module did not have the misfire that the original has. It simply ran for 5 seconds then refused to start, finally refusing to even crank the engine if I am understanding the technician correctly.
From my research and reading of online forums and what the technician relayed to me it sounds like security features have locked out fuel and starter relays.
Most of the posts I read suggest that the only way to eliminate the problem is to replace both the pcm and the bcm.
Now since both modules are basically computers I do not understand why unneeded features or miss programmed instructions or security features cannot be erased or turned off and properly reprogramed. In other words erased and started over again so that one does not have to keep purchasing modules until you get one that will work.