Snoke vs Rey - REMATCH

It wasn't a permanent amp. The dialogue clearly indicates it was a one-time thing. Rey was trying to connect with the Jedi from the past throughout the film. It was at that point in time she achieved it. They lent her their strength.

Ewan McGregor’s Obi-Wan: “These are your final steps, Rey. Rise and take them.”
Anakin: “Rey.”
Ashoka: “Rey.”
Kanan: “Rey.”
Anakin: “Bring back the balance, Rey, as I did.”
Luminara: “Find the light, Rey.”
Kanan: “You are not alone, Rey.”
Yoda: “Alone, never have you been.”
Qui-Gon: “Every Jedi who ever lived, lives in you now.”
Anakin: “Feel the Force flowing through you, Rey.”
Kanan: “Let it lift you.”
Adi Gallia: “Rise, Rey.”
Qui-Gon: “We stand behind you, Rey.”
Alec Guiness’ Obi-Wan: “Rey.”
Yoda: “Rise in the Force.”
Kanan: “In the heart of the Jedi lies her strength.”
Ewan McGregor’s Obi-Wan: “Rise.”
Qui-Gon: “Rise.”
Luke: “Rey, the Force will be with you. Always.”

Then there's the whole thing with her trying to connect with them to hear them, indicating she was in a very specific state of mind at that point in time. If it were a permanent thing, Luke and Leia - both Jedi who learned it - could call upon it anytime.

@BoD:

The dialogue clearly indicates it was a one-time thing.

Which is the thing in those lines of dialogue that makes you think it was a one-time thing? 
"These are your final steps" sounds to me like she is completing her training, and this is precisely what she was training for. 
"Find the light, Rey", "feel the Force flowing", "rise in the Force" and "let it lift you" indicate that she has to actively open herself and let the Force flow through her, with the line ""the Force will be with you, always" possibly implying that said Force will be there for her again.

Then there's the whole thing with her trying to connect with them to hear them, indicating she was in a very specific state of mind at that point in time.

She certainly has to enter a specific state of mind, but that's a requirement for every Force ability to work. You have to focus your mind in different ways. That's my interpretation anyways.

If it were a permanent thing, Luke and Leia - both Jedi who learned it - could call upon it anytime.

I don't recall it being mentioned that Luke and Leia learned to do it, but I may be wrong.

Snoke wrecks her