The issue that you are facing is primarily caused by the fact that your QA team is expecting single-page application (SPA) behavior out of (what sounds like) a multi-page application (MPA) design.
You are right to question altering the behavior of the back button because users have been taught to expect that if the page reloads as they "move forward" through an MPA, that and page that they have gone through is "in the past". And there are many MAJOR websites out there that behave just this way.
Now you can change that behavior and (1 - depending on the design of your overall site, and 2 - assuming that you address all of the potential issues involved with altering standard browser behavior), it might not be a drastic impact on user expectations, but, assuming that I am correct about the MPA design, you will be going against the standard MPA pattern/experience.
Some alternate options include:
Automatically take the user (forward) to an updated view of the previous page as a part of the confirmation that the new sprocket has been added. This allows them to see that it was properly added and reduces the likelihood that they will want to go back to the old version.
Consider updating your application to an SPA design, if you find that your requirement are beginning to push you that way. While this is likely a BIG undertaking to overhaul your application design, you are MUCH better off doing a redesign than trying to retrofit SPA behaviors into an MPA design.