Success! Looks like we've fixed this one. According to our records the fix was applied for
a bug in our system
a recent build.
Adding custom config functions or booleans is not possible
In Ext Designer currently some configs are missing, e.g. the grid column renderer. Adding them doesn't work, since my function is becoming a string. Please provide a option for custom config to create it without surrounding ''.
Please upgrade to build 309.
You can add renderer's to Grid columns now.