Machines per Operation in Part Master


I was wondering if there was any way to mass update the "Machines"
field on many BOMs. We have thousands of BOMs that on one particular
operation we need them to show 1 instead of 5.

We originally had that work center as needing 5 machines per op, but
have recently changed it to 1, but as jobs are created, they use the
default from the part master when they were originally created.

Any one know how to mass update that field?