The actress opened up to ET about her big plans for the character.
"I was so excited to do it because I've never done it," she told ET's Brooke Anderson during a visit to the film's set. But work got in the way of those injections. "I wanted to see what happens."
"I have a movie after this one... I start the next one three days after I finish this one, and that one is like I am going through a tragedy and really hard time. There's no makeup and no hair and I couldn't have had that leftovers [from the injections]," she explained.
The actress instead found more temporary ways to alter her appearance: through fake teeth and a big, red wig. "Maybe it's for the best," Hayek conceded. "Maybe I would have gotten addicted to it or something."
"Her character is so weird," Byrne explained of the dynamic Claire brings to the group. "You're not sure -- is she good, is she bad? She looks so crazy, it's great."
"She's very funny, Salma. She's really out there," she added.
"I'm more of a silent protester," Byrne revealed.
Haddish and Byrne make quite the comedic duo themselves -- though it's another quality that turned them into real-life friends.
"Tiffany is a magical person. She's very generous. She's very loyal and she's very fierce," Byrne gushed.
"And Rose be taking good care of me, be looking out, always compassionate," Haddish chimed in. "And she looks me in the eyes when I know I need to bring it down a notch."
They balance each other out on screen, as well as off. Byrne says she's a "silent protestor" when she gets into arguments with friends, while for Haddish, it "depends on what happened."
"Most of the time, if I feel like I was in the wrong or if maybe I don't feel wrong but I know it was wrong, they took it the wrong way -- I will apologize. But if they do something scandalous to me, well then I disappear," she revealed.
"I'm lurking on the Instagram but I'm not talking to you. I'll only like pictures of your kids and that's it," Haddish joked.
Like a Boss hits theaters on Jan. 10. See more in the video below.
'Like a Boss': Tiffany Haddish and Rose Byrne Take on Salma Hayek in First Trailer for Cosmetics Comedy