Q:

Selective inclusion of elements in BarChart Legend

Further to my previous question, is there a concise way - amenable to automated setting in a package so that it can be accessed globally - to eliminate some legend item that would otherwise show?  For example, in this example, I'd like to only show the orange rectangle and text "Preliminary estimates". 

I tried a couple of replacement rules, by analogy with belisarius’s answer for reversing stacked bar chart legends, such as the example below, but it doesn’t seem to make any difference. 
BarChart[RandomVariate[NormalDistribution[0, 0.6], 40], 
 ChartStyle -> Join[ConstantArray[Green, {39}], {Orange}], 
 ChartLegends -> 
 Placed[Join[ConstantArray[None, {39}], {"Preliminary estimates"}], 
 Bottom]] /. Pane[Row[x_]] :> Pane[Row[Last[x]]]

A:

Use MapAt to apply the Legended and Style wrappers directly to the last item in the dataset:
data = RandomVariate[NormalDistribution[0, 0.6], 40];

data = MapAt[Legended[Style[#, Orange], "Preliminary estimate"] &, data, -1];

BarChart[data, ChartStyle -> Green, LegendAppearance -> "Row"]

A:

The reason your code doesn't work is because the legends are typeset using a Row with two arguments (where the second argument is a separator which should be placed between the entries in the legend) but you're matching to a Row with only one argument.  You could instead do something like
BarChart[RandomVariate[NormalDistribution[0, 0.6], 40], 
 ChartStyle -> Join[ConstantArray[Green, {39}], {Orange}], 
 ChartLegends -> 
 Placed[Join[ConstantArray[None, {39}], {"Preliminary estimates"}], 
 Bottom]] /. Pane[Row[x_, ___]] :> Pane[Last[x]]

Edit
Another way to selectively label entries in the BarChart is to do something like this
BarChart[RandomVariate[NormalDistribution[0, 0.6], 40], 
 ChartStyle -> Join[ConstantArray[Green, {39}], {Orange}], 
 ChartLegends -> 
  Join[ConstantArray[
    None, {39}], {Placed["Preliminary estimates", Bottom]}]]

A:

Of course, this got a lot easier in version 9:
BarChart[RandomVariate[NormalDistribution[0, 0.6], 40], 
 ChartStyle -> Join[ConstantArray[Green, {39}], {Orange}], 
 ChartLegends -> Placed[SwatchLegend[{Orange}, {"Estimate"}], Bottom]]

