I tried several ways to install the update without losing the compatibility of Brazilian networks of telephony.
Honestly, I think the best way is wait.
There's a rumor that Samsung will release this update globally in early November. It's a rumor, but it's a possibility.
And the "second" best way, 'till now for us brazilians, is the interop unlock, but with some warnings:
1) Be warned that there's no return!!!! (Samsung doesn't offer a firmware recovery tool compatible with WP devices)
2) You won't be able to use the backup of your stuff (if you're doing the downgrade of the PFD) because it only works after a hard reset and the initial settings of the phone (wp 8.1 or higher) AANNNDDD.......
3) YOU WILL NOT BE ABLE TO DO A HARD RESET ON THE PHONE !! This will mess the CSC ZTO installed along with the ROM of GDR2, and the carrier's annoying constant messages will begin to appear.
If all those things don't bother you, go ahead.