...
Text callFromText = factory.createText(composite, "");
callFromText.addModifyListener(getCallFromListener());
...
private ModifyListener getCallFromListener(){

		return new ModifyListener() {

	    	@Override
	    	public void modifyText(ModifyEvent e) {
	    		String txtCallFromText = callFromText.getText();

	    		if (txtCallFromText == null) {
	    			txtCallFromText = "";
	    		}	

	    		final String txtNewCallFromText = txtCallFromText;

	    	IFeature feature = new AbstractFeature(getDiagramTypeProvider().getFeatureProvider()){	    				

	    			@Override
	    			public void execute(IContext context) {
                                        // transitions contains the bo asociate to pe selected
    					TransitionType transicionCall = (TransitionType) transition;
                                        // I can change the model here
    					transicionCall.setFrom(txtNewCallFromText);
	    			}

	    			
	    			@Override
	    			public boolean canExecute(IContext context) {
	    				return true;
	    			}
	    		};

	    		CustomContext context = new CustomContext();
	    		execute(feature, context);
	    	}

	    };

	}