cluster constant typedef cannot be edited?

I've created a cluster constant on a block diagram, then converted it to a typedef and saved it as a .ctl file. I need to edit the typedef to change several of the values. When I open the .ctl file in LabVIEW, I can change the values of interest, but when I save the file, the changes are silently discarded. What am I doing wrong? (Example attached.)

Thank you!