This example moves a control and assigns it a priority of 5 so that it will likely be dropped from the command bar if the controls don't all fit in one row.
Set allcontrols = CommandBars("Custom").Controls
For Each ctrl In allControls
If ctrl.Type = msoControlComboBox Then
With ctrl
.Move Before:=7
.Tag = "Selection box"
.Priority = 5
End With
Exit For
End If
Next