It all comes back to a company's quality plan for a product. What automotive calls
APQP is neither new or unique. We used the same process (with some additional steps) way back in the 1980's when I was in DoD work in aerospace electronics. The names are not the same, necessarily, but the parts of the APQP process were the same for all intents and purposes. We called them a QAPP - Quality Assurance Program Plan and I used to write them. All contracts were very specific in that any time we made the slightest change it had to first be approved by the customer (the DoD). Most of our processes had "qualified" operators so even a change in operators typically had to be pre-approved.
As to the original post, when you choose a supplier your contract review and approval process should include aspects such as how quality of the product will be controlled. Additional controls and things such as supplier process (or other) changes should be addressed. In my mind when ever a supplier makes
any type of change you are essentially going through a contract change which requires a contract review. No matter what they change, the customer must be advised prior to the change to give the customer time to evaluate the change and any potential effect it has.
There is no such thing as an "insignificant" change with the exception (in most cases) of a change in operator(s) of that process. And even there, often times personnel change can be a significant factor. Even moving a piece of equipment to a different place on the manufacturing floor can be a significant change.