October 20, 2015 01:00 PM

Sandra Bullock is describing her new role as a “once-in-a-lifetime opportunity” after the film’s producers changed the character’s gender so that she could take the part.

“It is a role like no other, it allowed me to do something different,” the actress, 51, says in a new clip from Our Brand Is Crisis exclusive to PEOPLE.

She adds that she decided to tackle the part because “you can’t repeat anything that you’ve ever done before, you should do things that are just scary and frightening.”

In the upcoming political satire, Bullock plays Jane Bodine, a world-renowned campaign consultant in a part that was original intended for her friend (and coproducer on the film) George Clooney.

Sandra Bullock in Our Brand Is Crisis
Warner Bros Pictures

“In our original script it was a man who was the lead protagonist,” producer Grant Heslov says in the behind-the-scenes clip. “And then Sandy had read it and she’s like, ‘God there’s no roles like this for us!’ And I thought let’s completely change it, let’s make her a woman.”

“The thing I loved about this role was that there didn’t seem to be any boundaries for the character both emotionally and in tone,” Bullock adds.

Bullock’s onscreen foil is Pat Candy, a political adviser for her rival campaign played by Billy Bob Thorton.

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“I love these adversarial relationships that also have just a hint of affection,” Thorton says with a smile.

“It makes a rivalry great and it also makes your desire for her to win greater,” Bullock adds in agreement.

Our Brand Is Crisis hits theaters Oct. 30.

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