Please everyone stop referring to this as PR1.2. This is NOT PR1.2 but a release candidate or testing build that has been leaked. It may have bugs not in the final PR1.2 build.

There is no way you can know this. I'm betting nokia isn't going to put a lot of effort into ensuring leaked builds for testing work with ota updates. And there may be bugs in the build that prevents updates. It may turn out that it works, but there is no way you can be certain until the real PR1.2 is actually out and you can test updating to it.

Anyone using this leaked build has to accept the risk that they will have to do a full flash once PR1.2 is out, and that backups made using this FW may not restore properly once the phone is updated to PR1.2. If you can live with that then by all means play with the new toy, but don't give other users guarantees that you can't know to be correct.