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 contain attributes for rich text field along with their character limits. For example, the attribute for Description is longDescriptionRichText (HTML text). You can edit the character limit for the required attributes.