Stacy Keach is the latest addition to the cast of Universal’s “The Bourne Legacy.”Written and directed by Tony Gilroy, the pic stars Jeremy Renner, Rachel Weisz and Edward Norton. Plot details are being kept under wraps, but Jason Bourne will not be featured in the film, while Renner will play another assassin trained in the same program as Bourne. Frank Marshall, Ben Smith, Jeffrey Weiner and Pat Crowley are producing. Jennifer Fox will exec produce. Variety first reported that Joan Allen and Albert Finney would be reprising their roles and Keach would have a similar role in this installment. Keach was most recently seen in the FX series “Lights Out.” He is repped by Lionel Larner, Binder & Associates and Mitchell Silberberg & Knupp.