FYI I've been trying to assign the part number of the parts to a global variable then assigning a global variable in the assembly to the parts PN global variable however can't get it top work because of multiple configurations with different PN.
I've also got the part's PN in an annotation in the part file that I make visible in the assembly file and it changes like it should when I change the part configuration in the assembly. If I can link the assembly part number to the annotation that would work perfect, however I cant figure out if that's possible.
Try to use the chain: Part Global Variable ->Assembly Global Variable->Configuration Specific Property - Assembly Part Number.
Design Table may be very helpful too.