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GridTable table = this.gridGroupingControl1.GetTable("ChildTable");
table.TableDescriptor.Columns[2].HeaderText = "SomeReallyLongName";
adjusting the column width for the longer title. Exactly how are you modifying the visible columns?
You might try calling
GridTable table = this.gridGroupingControl1.GetTable("ChildTable");
table.Reload();
this.gridGroupingControl1.Refresh();
to see if that does what you need.