I remember reading in a summary that in one Avengers story arc...I think the "Evolutionary Wars" Hercules fought the High Evolutionary and was evolved into something "beyond godhood." Was it ever elaborated as to what that was and how Hercules returned to his normal state?

Hercules was returned to his normal state when Thor found Hercules' essence/spirit being used by the Celestials in some sort of construction/experiment in the Black Galaxy. This story arc took place in "Thor" #419-425 and has recently been collected as a trade paperback.

As far as anything Herc did while he was evolved "beyond godhood" : He did nothing (aside from defeating High Evolutionary at the end of the Evolutionary War), really. When Hercules returned to his traditional immortal Olympian God form he did so without displaying any power or performing any feat that could even remotely be worthy of one evolved beyond godhood. He simply returned looking pretty much like he always had except he was missing a key part of his psyche the Celestials has kept - his enormous courage. The story was kind of a rehash of an earlier arc in Thor (approximately 15 years earlier) where Hercules had lost his courage and confidence to the Dweller in the Darkness.

Even though Herc was only evolved beyond godhood as a plot device to defeat the High Evolutionary, empowering him that way was a great opportunity to use Hercules on a grand/epic scale. That didn't happen. The opportunity Hercules was given (the Marvel writers and editorial probably didn't even consider it an opportunity) was squandered when he was brought back without any further use of his evolved powers.