If the Cart' is enjoyed in the current condition, and the only requirement by the owner, is to have a new stylus added.
A return of a Cart' to a manufacturer might not offer a service that is limited to replacing the stylus only.
On returning a Cart' to a manufacturer, there is a possibility that the service will incorporate more than the exchange of the stylus only.
If the Manufacturer is changing other parts used in the Cart's assembly, there is the possibility the Cart' can be returned to the owner with a material added that is 'equivalent' in function, but not the same to those it was sent with.
The longer the Cart' has been owned, the more likely the Manufacturer has been sourcing different components for modern generations/variants of the Cart'.
I do believe that their are Manufacturers that are very considerate to their customers and do concern themselves with being able to keep a Cart' true to the era it was produced.
It would be good to know of considerate manufacturers, that would keep a stock pile of earlier generation parts, apart from a styli, to be used on returned Cart's from the earlier generation productions.
There might be a detection by the Cart's owner, that the returned Cart', if incorporating new parts, is being perceived as having a sonic difference.
My experiences encountered, where there has been comparison demonstrations of different Stylus Forms used on Ortofon Cartridges, that are from different production era's, but share similar methods used for the Cart's designs, is that the assessments made are leaning toward the Stylus does not appearing to be solely responsible for impression the Cart' can make.
The differences detected in the presentation of the variations of the Cart's being demonstrated, is most likely caused by choices of materials selected for the overall assembly of the Cart' and the methods used for the assembly.