The school of thought that appeals to me the most, is the process where once the design transfer occurs the DHF is sealed. I say this mainly because I only have experience doing it this way. After the design transfer, any changes to any design specifications, or software updates must undergo a Design Change Process (DCP). In this it details the change, what is being affected, what inputs/outputs are affected, the risk, priority level, and a verification/validation that verifies that the change has been implemented.