The 24-year-old is Penn State's first portal addition.
Stewart is the second Nittany Lion to enter the portal on Wednesday.
Penn State Police said the situation has been resolved.
Blackwood appeared in 26 games for Penn State in 2025-26.
Penn State has landed its first four-star recruit in the 2027 recruiting class.
With Alex Manske out for the spring and Rocco Becht slowly returning from injury, Penn State's quarterback unit is in a unique position.