You can't reactivate something that was never deactivated in the first place.
This is true.
The IFE has always worked on the 757-300s, they just only used it for the HNL flights.
That's deactivated. I think you're confusing 'deactivated' with 'disabled'. Deactivated means in a condition where it could be used but not actually used, disabled means in a condition that it can't be used.
The IFE was totally removed from the 320s and the moldy oldy 757, 5500 series. The rest of the domestic fleet never had IFE.
That's removed.
Using systems that were previously not used is reactivating.