Usually one wants to make the change persistent in the sources. Step a): One just evaluates from the sources, while changing them. Once done -> save sources.

Usually one wants to make the change persistent in the sources. Step a): One just evaluates from the sources, while changing them. Once done -> save sources. Step b): Create a patch file, which changes the image. Such a patch file can be loaded while starting an image, until one decides to save a new image with the changes already loaded. For example there is a new release for the commercial LispWorks IDE once every one or two years. Users usually get only patch files for bug fixes during the one or two years maintenance. Thus I have a directory for patches to LispWorks, which are loaded when I start the base image.