WORKAROUND
A possible workaround for the issue is to use a custom customizer and the following code:
public class CCCMyCustomizer: StateLessEntityLogic
{
public CCCMyCustomizer ()
{
CanEdit ( "extensionAttribute3")
.From ( "extensionAttribute2")
.As ((string ext2) => ext2 == "A");
}
}
This must then be delivered via DialogFileRevision, made known in the dialog and assigned to the table.
STATUS
There is no fix for 7.x or 8.0.x as it would result in a code breaking change. A fix is available in 8.1 in the way of two new columns, DialogColumn.CanEditScript and DialogColumn.CanSeeScript which can now be edited in Designer.