They released a longer version in recent years with a few scary scenes put back in and the original ending, which was lousy in the first place. The "spider-walk scene" that I'd been hearing of for years was definitely good. Sadly, they've never found the original footage of an early scene shot at Arlington National Cemetery, which made the social subtext about the culture clash a bit more evident.
As one might suspect, given the 70s release, there was indeed a disco version of the theme song released, and a blaxsploitation remake; sadly, it was not entitled "The Blaxorcist". It was called Abby and the studio sued to get it taken out of general release. Here's a scene set in a nightclub.
If I ever own a cell phone, I think "Hellllloooooo Motherfuuuckerrrr!" will be my ringtone.