However, as intriguing as that is I don't guess it happens overnight. So if used the a red dwarf that transitioned to blue that transition probably would not happen during the recorded history of the Frontier. 

I suppose what you could do is have the previously habitable tidally locked planet is now baked out but there are ruins of its previous civilization. There is a new even more lovely habitable planet in the system.

EDIT:

The Previously inhabitable planet is baked out and the ruins of a dead civilization are plain to see. It seems that this civilization managed to move to the newly inhabitable world. The mystery is the tech of this civilization is not advanced enough for space travel. The population growth number, worked backward point to zero population at about the time the astrophysicist say the star transitioned. The legends of this civilization claim "god or gods" judged them with fire but a select few were brought to "heaven".  In fact when the first exploration craft landed the sapients asked the explorers if the were their societies analog if angels or devils. The explorers denied both but the jury is still out as far as the locals are concerned though there is a strong current of thought that suggests that the visitors (core four) are most likely devils ( and of course there has been some behavior displayed by members of the core four that is easily cast as devilish after all it will be impossible to keep corporate reps from showing up. ).