The work item channels displays the work items in the order specified by the selected query. This means that you can control the sort order by modifying the query’s sort preferences. You can do this from Team Explorer, expand Work Items to your query, activate context menu and select View Query, and then click the Column Options button on the toolbar. From that dialog, you can define the sorting order.
The fields however cannot be changed in the Pending Changes window. Why? We had a usability study back in pre-V1 and the results were to keep the channel simple.