In Planner, you can choose from two options to edit a work item:Overlay editor and In-place editor.

Both perform security checks, so you will only be able to see or edit the fields which you have enough permissions for. To open the overlay editor, click any work item key in the center pane. If you do not have enough permissions to edit the item, a simple read-only listing of the fields will appear.

To open the in-place editor, click the gray outline that appears when you hover around the fields in the center pane. You will then see their corresponding input field inside the item listing. From there, you can use the Esc and Enter keyboard shortcuts. Esc discards your changes and exits the in-place editor, while Enter saves your changes and exits the in-place editor.

From Codebeamer 9.1 in-place editing is working for almost all of the fields (table fields are not supported) - of course if you have permission to edit the field. Built-in read-only fields are not editable (Assigned at, Submitted at, Submitted by, etc.)

From Codebeamer 9.3.0, in-place editing is also supported on the Details panel of a work item (on the right-hand side area of the Planner)

You can create new Downstream References for items by using the context menu next to the Summary field, and selecting a tracker under the Create Downstream Reference menu option.