Is it possible to rollback a module?

Question

Modules can be installed in different versions; it is recommended to keep only the latest version of the module, to have a clean environment. 

Answer

And old versions of modules can be started when the definition is backward compatible. This means when the content matches the definition of an old version of a module, it can be installed or started. 

When you install a new version of a module, you can get a warning about definition changes. If you have this warning, you have to validate the definition. Maybe a migration of the content is needed so that it will work with the new definition.

In case of definition changes, read the Jahia documentation carefully:

Jahia 8.1.x: https://academy.jahia.com/documentation/jahia-cms/jahia-8.1/developer/creating-and-managing-content-types/managing-definitions/modifying-existing-content-definitions

Jahia 8.2.x: https://academy.jahia.com/documentation/jahia-cms/jahia-8.2/developer/creating-and-managing-content-types/managing-definitions/modifying-existing-content-definitions

Also when you move definitions to another definition file or module, you have to clean the definitions on the environment. See: https://academy.jahia.com/training-kb/knowledge-base/moving-definitions