Idea definitions can be changed on the system by clicking on Ideas -> Select the Idea then click on Definition and select the new required definition.

After the Idea definition has been changed the Idea will automatically be subjected to the following changes.

• The Idea will immediately be moved to Evaluating.
• All previously approved workflows will be cancelled, and the respective Stage dates deleted.

Also, note you can use this functionality to update the details of the current definitions if there was a role or workflow deleted on administration -> Idea definitions -> Workflows. 

You can select the same definition and the new details will be pulled through and mapped to the Idea.