ASU change of major after frosh admission to an engineering major is not restricted, but students who enter ASU outside of engineering must meet the listed transfer requirements at https://engineering.asu.edu/admission-requirements/ (change of major at the bottom of this page).
As an aside, he may want to consider whether he wants to do a more specialized major like aerospace versus a more general major like mechanical (with aerospace electives). Aerospace leads to a more limited set of employers and jobs (many of which require security clearances), although the competition for those jobs will include other types of engineers. Non-aerospace jobs may prefer those with a more general major like mechanical.
Within California, did he apply to UCs and CSUs where the engineering majors are not impacted or less impacted (e.g. UCR, UCM, CSUSac, CSULA)?