Run code, press button.

import javafx.application.Application;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.control.cell.CheckBoxTreeCell;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.util.Callback;
import javafx.util.StringConverter;

public class Main extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        VBox vb = new VBox();

        final TreeView lv = new TreeView();
        lv.setRoot(new TreeItem(new DataItem()));

        Button b = new Button("Press me");
        b.setOnAction(new EventHandler<ActionEvent>() {

            public void handle(ActionEvent t) {
                Callback<TreeItem<DataItem>, ObservableValue<Boolean>> callback1 = new Callback<TreeItem<DataItem>, ObservableValue<Boolean>>() {

                    public ObservableValue<Boolean> call(final TreeItem<DataItem> p) {
                        return p.getValue().someData;
                    }
                };
                lv.setCellFactory(CheckBoxTreeCell.forTreeView(callback1, new CellCustomStringConverter()));
            }
        });

        vb.getChildren().addAll(lv, b);

        Scene scene = new Scene(vb, 300, 300);
        stage.setScene(scene);
        stage.show();
    }

    class DataItem {

        public ObservableValue<Boolean> someData = new SimpleBooleanProperty(true);
    }

    public class CellCustomStringConverter extends StringConverter {

        public static final String TO_STRING_PREFIX = "tsc ";
        public static final String FROM_STRING_PREFIX = "fsc ";

        @Override
        public String toString(Object t) {
            System.out.println("Called to string");
            return TO_STRING_PREFIX + t != null ? t.toString() : "null";
        }

        @Override
        public Object fromString(String string) {
            System.out.println("called from string");
            return null;
        }
    }
}

I expect to see "tsc " prefix before presented items' names.