So installing a beta OS is approved but changing the CSC which loads carrier specific settings that are already loaded but not activated voids the warranty? Sounds like the shop does not know what they are talking about.
Is the shop assuming that you are flashing the device?
Changing CSC, does
NOT void your warranty, cuz you can always change it back to your carrier's CSC. Any service shop (or Carrier tech service) who will say to you that by changing your CSC you voided your warranty is doing that cuz of 2 things:
1.
Doesn't know what they're doing.
2.
Doesn't want to repair your phone.
By flashing a new ROM over OTA, also is not considered as voiding your warranty cuz that's the
OFFICIAL way, but if you side-flash a new ROM, that will void your warranty cuz those are considered
custom ROMs, which in this case to be able to do that, you will have to have your phone "jailbreaked" or in other words, has to be interop-unlock, which
WILL void your warranty.