If you are returning a paper item, you will do what you have always done.
If you are returning an image, it will be accompanied by an xml file based on the 9.37 standards Bill mentions. In that file you will indicate a reason for return. The image will not be affected. However, if it is necessary to print that image as a substitute check when the image gets back to the depositary bank, the reason for return will be extracted from the xml file and appear on the face of the image as printed on the substitute check.
In short, you don't need any new stamps.