If you ever made some architectural visualization with Blender in the not so distant past, you probably have already used some external render like LuxRender. I have used both LuxRender and YafaRay a lot, and some of my oldest projects were all rendered with them. When a client ask for a change on any rendered image my first reaction is to analyze and try to make the change with an image editor. I want to avoid a new render at all costs! But, it not always possible. For those situations I have all legacy files and softwares on my backups.
One day I will start to convert those projects to Cycles just like an artist called camera just did! He posted a set of images from a project called House Vilamar, which was originally created with Blender and LuxRender and he did manage to render it again using Cycles. Visit the forum for more images of the project.