Rich text attributes are extended for the fields Description, Reason, and Proposed Solution. The default character limit for these fields is set at 20000. To edit the character limits, you need to update the Info*Engine tasks for the given summary reports stored on the path <WINDCHILL_HOME>/Windchill/tasks/com/ptc/windchill/enterprise/change2/reports:

The XML files display three attributes for each rich text field along with their character limits. Each attribute denotes the component that it uses: simple text, HTML text, or rich text. For example, the attributes for Description are longDescriptionPlainText (simple text), longDescriptionRichText (HTML text), and longDescriptionCognosRichText (rich text). You can edit the character limit for the required attributes.

After updating the Info*Engine tasks, execute the given command in Windchill shell to automatically update the character limits in Cognos: