Charles pulled out of the tournament due to personal reasons, opening the door for Hendricks to join the squad.
The 36-year-old South African previously played in the PSL for Multan Sultans in 2024, scoring 304 runs at an average of 43.42.
Fraser-McGurk, who was set to represent Rawalpindiz, has opted out before making his debut in the league. The franchise has said a replacement will be announced in due course.
Karachi Kings will open their campaign against Quetta Gladiators on Friday, while Rawalpindiz are scheduled to take on Peshawar Zalmi on March 28.