Testflight - continue testing after 30 days?

We are looking at running a test campaign for our iOS mobile app with a few hundreds users, using TestFlight.

(We cannot use an Apple Enterprise account)

The test will last 50 days and there is a 30-day limitation for test flight builds.

the documentation says:

To continue testing after the 30-day period expires, upload another build. Internal testers automatically receive an update notification when the new build is available. To distribute the new build to external testers, you resubmit it to Beta App Review. As soon as it is approved, you can send the external testers an update email by clicking Send Invites from the External Testers column on Builds,

http://ift.tt/1q7sA2H

So, in theory, we could test version 0.9.0 for a month, then build and distribute 0.9.1 and have people update (yes a little clunky).

The question is does it really work and what happens to local app data when updating? things like coreData and NSUserDefault?

It would be great to have some sort of absolute confirmation than those are fine.

I cannot fully test that because update behaviour might be different before and after passing that 30 days limit.

Thanks in advance.