The "problem" with any customization is there may be "unexpected consequences", hence why CA regard them as unsupported - which is fair enough really.
As a general rule one should expect to have to reapply (or at least investigate whether you need to reapply) any customization after upgrade (and indeed remove any customization before upgrade).
I would think that its reasonable to expect an upgrade to redistribute the server properties files, so I personally would expect this sort of particular customization to need reapplying after upgrade (unless CA have changed the translation to your satisfaction as part of that upgrade - i.e. some investigation is always required!). I would suggest that any customisation is well-documented - what/why/when to remove/how to revert etc as part of the local installation's "knowledge base" - the local support team will need all this information on an ongoing basis.