Background Pony #034D
Now that it's been several months since the movie dropped, I think it's safe to say that her power up is indeed "permanent". Remember, just because she can turn it on and off doesn't mean it's temporary. Temporary would imply her alicorn magic running out and wait to gain more. She's still an alicorn on the **inside**. The rainbow streaks on her hair prove that she still has that power. She can turn it on and off in any situation. While Hasbro currently has no plans to have her an alicorn 24/7 (meaning with actual physical wings and horn like Twilight) this is what they're sticking with.