They are not difficult too change and there is no special tools required. But a little grease will take care of the problem. Eventually the new bushings will require little lube as well. In fact what you will probably find is where the bushings sit around the bar, is a little corrosion of the bar. Taking a wire wheel to the bar and cleaning it up and then a little grease will take care of the noise.
Personally, I perfer to not change parts unless they really need it.