If I have to pick a point in the series that Harry goes back in time it would have to be Changes. During the chaotic battle, someone yells Fuego. Additionally, there is the time gap after he kills Susan. My assumption is that future Harry is there to stop someone from reversing the end of the RC. Harry being Harry can't help seeing Susan one last time before she is turned. That is when he the two Harrys meet. The time lapse is the result of mental magic. Thus, Harry breaks two laws of magic. The mental magic could fall under a technicality loophole since he is only doing it to himself.

Can Luccio make a sword that can cut through Lucifer's magic? Possible but doubtful.

I think that we will find out Mac is a retired wizard who gave up the magic for normalcy.

I can go with Cowl having to do alot of prep work for the Darkhallow. The magic drugs, the tormented ghosts, and the spalttercon fearfest are good ways to create a spiritually- heightened state in Chicago.

A young John leguizamo would have been perfect.

Jason Isaacs fits best as Marcone.

THere is the additional fact that Elaine has learned a bit of healing magic. So, I think she learned it from Joe and she is Kumori.