Is it possible to rename a panel after it is created?

If by panel you mean ‘data source’, then yes. Close all your existing panels using the “Windows->EasyCatalog Panels->Close All” menu option. Then locate your ‘EasyCatalog Workspace Folder’ via the Reveal button in the InDesign->Preferences->EasyCatalog section. Then just rename the appropriate folder in there and open them from File->New->EasyCatalog Panel