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Kevin Costner 's lawyers want the lawsuit alleging he made a stuntwoman participate in an unscripted rape scene dismissed ... because he says the stuntwoman suing him has changed her story ... essentially admitting she lied in the original complaint.

The actor's lawyers filed more legal docs in the case ... and, now they're pointing out Devyn LaBella -- a stuntwoman on "Horizon 2" -- previously claimed she was thrust into the movie's rape sequence without any discussion beforehand. Getty

However, they point out she now admits another individual -- stunt coordinator Wade Allen -- "met with her in advance and explained the shot to her in advance."

Costner's lawyers also say LaBella's admitted before she blocked the shot, she knew the basics of what would happen, including

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