Change OrderDtl when Customer on OrderHed Changes

I am trying to change a UD field on all Order Details of a Sales Order
when the Sold To Customer is changed. I've tried customization and
BPM. The problem with the BPM is that I can't get it to access the
ttorderdtl table when the Customer changes on the OrderHed table. The
problem with a customization is that if I try to change the value of a
field in the orderdtl from the OrderHed change event, then I can't save
it because it thinks the order has been updated by another user.

Anyone have any ideas how to occomplish this?