Morgan Creek Productions fired Paul Schrader after he had submitted a completed movie, saying that he had given them "footage without any of the bloody violence the backers had wanted". He had already made it clear in interviews that he was making more of a psychological drama than an all-out gore-fest. He was fired and Renny Harlin was hired to re-shoot the movie. Almost 90% of the movie was re-shot and at least two characters have been dropped from Paul Schrader's version of the movie. Following the lackluster reception to Harlin's version, though, Schrader's version was finally released as Dominion: Prequel to the Exorcist (2005).
After Merrin has opened the lid of the crypt inside the church, and he lights the crypt, the face of the demon can be seen for just a few frames on the inside of the lid. A same technique of blink-and-you'll-miss-it appearances of the demon's face was used in The Exorcist (1973).
The film was originally rated NC-17 "due to the film being too graphic and violent". The offending scenes were edited and the result was the R-rating for "strong violence and gore, disturbing images and rituals, and for language including some sexual dialogue".
When Morgan Creek hired Renny Harlin, he told them that Paul Schrader's version was complete crap and unsalvageable, and without any intention of actually signing onto the project, said that they'd be better of re-shooting the project from scratch. Much to his shock, James G. Robinson, the head of Morgan's Creek, agreed to this and offered Harlin an even bigger budget and paycheck than they had given Schrader. Harlin accepted the offer, and rewrote the screenplay alongside new writer Alexi Hawley.
Warner Bros. pushed Paul Schrader into adding more gore than he really wanted to. Matters came to a head after Schrader turned in his first edit however - the studio promptly fired him, as they thought the finished product was too slow, too talky and still wasn't gory enough for their liking.
Several changes followed the firing of Paul Schrader, both in crew and cast. Screenwriter Alexi Hawley was called to retool the previous script, and he cut off some characters of Paul Schrader's version, besides adding some new ones, like the one played by actress Izabella Scorupco. Actor Gabriel Mann, who played Father Francis in the original version, was not able to re-shoot his scenes due to schedule problems, so new director Renny Harlin replaced him with James D'Arcy.
The screenplay had a long and painful gestation process. William Peter Blatty refused to get involved, resulting in over a decade being spent trying to get a screenplay together, with the producers eventually settling on a draft by Caleb Carr, which incorporated elements from an earlier screenplay by William Wisher.
It is well reported that Morgan Creek fired Paul Schrader and then hired Renny Harlin to shot the film from scratch. However the trailer used for Harlin's reshot version is made up of footage completely comprising of Schrader's original cut. So, bizarrely the studio spent millions of dollars on a completely new film but never went to the trouble of changing the trailer.