Downgrading is supported.
Check Downgrading topic for details.
Customizing Version Field mapping
From a Jira work item, resolution of Global Configurations involved in OSLC links depends on link types and associated Jira Version Fields. The standard mapping associates link types to either Affects Versions or Fix Versions fields, based on the link type semantics and how engineering teams work across applications. This standard mapping is logical and is recommended to use in most cases. Starting with this version, if an organization has a need to change the Version Field used for Global Configuration resolution, a Jira administrator may choose to customize the Version Field mapping of a given Jira space. See Version Fields for Global Configurations for details.
Downgrading is supported.