At Philips IGT, we develop and produce interventional X-ray systems. For a controller in these systems, we have an approximately five years old domain specific language. Like general programming languages, domains specific languages also evolve. These languages co-evolve together with their domain. The language used at IGT was initially created for one system instance. Because of our positive experiences with the language, we want to evolve the language to support a family of systems. In this paper, we report on our experiences with the modifications we made to the original language. We made these changes preserving the behavior of the existing system instance. To prevent confidentiality issues, we use a Lego robot in our examples.