Model Driven Engineering provides powerful solutions for the development of User Interfaces. However, concepts and techniques are difficult to master and to apply: the threshold of use is said to be high, making designers and developers reluctant to use it. This paper investigates process model flexibility as a solution. We present three kinds of flexibility for improving design and development process models: (1) variability for equivalent choices, (2) granularability for several levels of details, (3) completeness for possibly optional and pre-defined reusable components. Flexibility decreases the threshold of use by reusability of knowledge, know-how and pieces of code. We illustrate these forms of flexibility on an industrial case study from the nuclear power plant domain. We explain how they are implemented in FlexiLab, a running prototype based on OSGi. The innovation is twofold: on one hand, the operationalization of flexibility; on the other hand, the jump from simple applications to real case studies thanks to flexibility.