His arm wasn't the only thing the Galra changed. They also gave him certain... needs. Shiro learns to make it work for him.

No one would help him get to the bottom of Kerberos, and it had all reached a breaking point when Iverson threatened to terminate Keith’s scholarship if he kept snooping. So Keith got what he came for, the little black book no one was ever meant to find, and stopped snooping. Because now, he’ll have someone else to do all the snooping for him. The situation isn’t ideal, Keith thinks as he slits his palm open and methodically draws the pentagram on the floor, placing the necessary items one by one into each point of the star. But considering the circumstances, he thinks he’s done alright for himself. More importantly, for Shiro.

“I still - I don't-” Shiro feels like his brain is broken. “I still don't get why this is necessary.” “All aspects of physical stamina are tested during the trials,” Kolivan replies, standing next to him as both of them watch the screen. “Awakening the blade is only the first step. Your friend is an omega, and all omegas currently serving with the Blades have lasted an hour or more on this device. It is protocol.”