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CICS Supplied Transactions on the IBM web site and you could read this for yourself. All quotes are from this manual:
Use CEDA to define resources to your CICS system while the system is running. With CEDA, you can update both the CICS system definition (CSD) file and the running CICS system.
When you use the CEDB transaction, the INSTALL command is not available to you. This means that you can update the CSD, but not the running CICS system.
The CEDC transaction allows you only to look at data on the CICS system definition (CSD) file. You cannot update either the CSD file or the running CICS system.