Will the bought TV series be kept after changing the store country?

Copies you've downloaded to a computer will remain available, but you won't be able to redownload them from the new country's store.

(192976)

No. You can only stream from what is available in the Store for your region.

Here's what Apple states about this, and about what media might or might not be available:

Change your Apple ID country or region - Apple Support

If you have media that you really like, purchase a DRM-free copy of that media assuming you can locate same.

aka-0110 wrote:

In case there were no copies downloaded to a computer, would the TV series BOUGHT in the country A’s store be still available to be PLAYED in streaming after relocating to country B (whose store doesn’t have such TV series available)?

Nope. Or as was mentioned earlier, if you have media that you really like, purchase a DRM-free copy of that media assuming you can locate same.