Can the Generac XT8000E be permenantly installed indoors with exhaust extended to outside?

No, unless you want to die in your sleep. Besides it being illegal, you cannot vent ALL the carbon monoxide outside. Like a car in a garage where the exhaust is vented outside, eventually you'd die. Service stations will do it for a few minutes, but that's it.

Yes, this product can be used in that manner.