I have a prewar Admiral "camera style" portable with a Tenite case. The Tenite is in fairly good shape, but is warped slightly were the case halves separate. I'm fairly sure that some heat carefully applied followed by restriction of the case will bring the halves back into better alignment. I have a candy thermometer I can use to monitor the temperature. My question is how much heat is too much. Has anyone had success manipulating Tenite?

Tenite is just like any other plastic, you can heat it and manipulate it
I fixed a tenite face on a Silvertone tabletop on time by gently heating it and flattening it.
I also have fixed a few tenite grills on some small Philcos. They worked out great. I heated and stretched them and bent them back into place with a small craft style heat gun.
I also ruined one by doing the same thing. Got it too hot and it became discolored and a little "crusty" (like burnt) on the grill face. I cleaned it up the best I could but it bummed me out that I did that

as for the temp, can't help you there.
just do it slowly and methodically taking small baby steps

~jeff~