Transferring saves between different-region versions on same account

I purchased Horizon: Zero Dawn abroad and played it on my Brazilian console and account. I really enjoyed it, so I purchased its Frozen Wilds DLC, only to discover that DLC is region-locked. So Brazilian DLC with non-Brazilian disk means I just threw money away.

Now, one solution would be to buy a Brazilian disk (or download the main game via the PS Store). I don't know if I'm willing to pay full-game price for some DLC, but let's assume I am.

However, that leads me to my question: would I be able to transfer my save from the international version to the Brazilian one? I know saves can't be transferred between accounts, but this would all be on the same account on the same console, just between different "versions" of the same game.

I just don't want to invest more money on this game only to discover that the DLC now works, but I have to start from scratch because I can't transfer my save between "disks".

Unfortunately, there is no official way to accomplish this. I can't speak for DIY solutions, but I doubt there's much in that way. The very simple reason is that a game from a different region has a different internal code.

The only solution in your situation, keeping your savefile, is to create an additional PSN account in the region that your base game is in (for example, USA). Then, purchase the DLC in the appropriate PSN store. Afterwards, you can safely swap back to your original PSN account. The DLC should be available for play.

If you don't mind losing your savefile, your options are indeed as you stated - buy a new disc, or buy it digitally.