Nickal was originally set for fight Tresean Gore before Gore pulled out due to injury.
Sturtz spent three seasons at Penn State as a forward from 2015-18.
The Nittany Lions will open the season against Le Moyne at Jeffery Field.
Penn State's global ranking of No. 83 is a bump from last year's ranking at No. 93.
With some notable commits seeing upgrades in their ratings, the Nittany Lions can let their top players develop without adding more recruits to the class.
Across seven games for Friendship Collegiate Academy in 2022, Cook registered seven total tackles, including six for a loss, according to MaxPreps.