MySQL 5.7 Reference Manual
MySQL 5.7 Release Notes
Downgrade is only supported between General Availability (GA) releases.
Downgrade from MySQL 5.7 to 5.6 is supported using the logical downgrade method.
Downgrade that skips versions is not supported. For example, downgrading directly from MySQL 5.7 to 5.5 is not supported.
Downgrade within a release series is supported. For example, downgrading from MySQL 5.7.
zto 5.7.yis supported. Skipping a release is also supported. For example, downgrading from MySQL 5.7.zto 5.7.xis supported.