So I just finished up Episode 3 and I was hoping that I'd be able to go back through Eps 1-3 in order to play the missions on HC (for the titles and SG) but unfortunately, that wasn't possible. Is there no current way to go back through them or am I stuck without those rewards for wanting to get through the story?

Click the dropdown above the story quest list. Note that in the below image, the drop-down says "All" at the top:

Oh man. I had no idea that was even a thing. Thank you!