Is there any way to add or modify the canned reports in WCC 11.4.x and is there a description of what each report shows?

Release: ATSYHA99000-11.3.6-Workload Automation AE-High Availability Option
Component:

The following link is for general details about the WCC reports:
https://docops.ca.com/ca-workload-automation-ae/11-4-2/en/monitoring-and-reporting/ca-wcc-monitoring-and-reporting/ca-wcc-reporting-application/predefined-server-statistical-and-job-run-activity-reports

For a more detailed description of what each report is intended to display, including the documentation for the autoaggr command as it compiles the data that the reports use, see the following:
https://docops.ca.com/ca-workload-automation-ae/11-4-2/en/administrating/ae-configuration/retrieve-aggregated-job-alarm-and-scheduler-statistics/statistics-reported-by-the-autoaggr-command

The predefined templates allow you to create reports from them. Depending on the type of report, there are options you can configure to customize your report. Such as choosing which AUTOSERV or job name to include or what time frame. See the following for more details:
https://docops.ca.com/ca-workload-automation-ae/11-4-2/en/monitoring-and-reporting/ca-wcc-monitoring-and-reporting/ca-wcc-reporting-application/generate-a-report-in-the-reporting-application