Since version 10
The steps to perform a counterfactual analysis are described in the article Causal Inference.
One of the steps, called Abduction, can be made easier using the Abduction dialog in Bayes Server.
In the sample network Counterfactuals BOW the variables Uex and Us are known as characteristic variables. These help us capture idiosyncratic characteristics of an individual/item.
The abduction step simply queries the current values V for the characteristic variables, given the current evidence. It then removes the evidence corresponding to the current individual/item, and then sets evidence on the characteristic variables to V.
See Counterfactual analysis for detail on all the steps required to perform a counterfactual analysis.
Although it was possible to perform abduction manually in versions prior to 10, the Abduction Dialog simplifies the process.