If a change can be implemented by modifying only a few of the layers (typically metal) then the cost is much less than it would be if the design was re-built from scratch.
In this flow, engineers manually (and often tediously) hand-edit the gate-level netlist, instead of re-running logic synthesis.
It uses formal equivalence checking and logic synthesis techniques to produce a gate-level ECO netlist based on the changed RTL.
[5] The telecommunications industry has a formal process that takes elements of the ECO and other considerations and combines them into the "product change notice" (PCN).
As a result of implementing these changes – regardless of who performs the actual work – the telecommunications carriers are significantly impacted with respect to labor and resources, etc.
Fundamentally, the customer's goal is to ensure there is a process by which there is accurate and efficient tracking and reporting of changes to products.
The entire PCN process is documented in GR-209, Issue 6, Generic Requirements for Product Change Notices (PCNs).