Been while since we were on 11.3 but I think the following functionality is there:
In Define, right click on the application and select Save As... to save it as an XML file.
Use a text editor (Notepad++ or something similar) to Find/Replace the variable in question ( replace 'A1 A2 A3' with 'A1 A2 A3 Y')
In Define, right click on the Server connection and choose Open from File...
Upload the new application.
Getting the application out and back in could also be don with the export/import utility
DE is quite picky about the XML structure and if that is modified it will either not open the file or you may see jobs with red icons indicating a problem. You will not be able to upload the application if these problems are not fixed. Better to take care to not modify the XML structure and ensure you are only changing the content.