Edison made "perspiration" a hero and popularized the role of persistent action in innovation. He was role model for incremental improvement. He would have understood that Big Bang approach to software modernization might not always be possible.
Partial modernization of existing software is a highly viable option, and addresses different parts of the software in isolation for the rest and modernizes that part alone.

SOA enablement can be done without transforming the entire application. SOA doesn't have to be complicated, but it is important to have a clear SOA strategy. While it is indeed possible to use a Web Services wrapper to extend the life of your existing applications, without a clear understanding of the security risks, you could be looking at potential disaster.

Web enablement is a common partial modernization strategy. The Web browser has become the standard, universal, intuitive interface, replacing both GUI and text based interfaces as the interface of choice. Many businesses are completely reliant on older interfaces. Simple web enablement of mainframe data and applications can provide a tremendous boost in service quality and productivity.

Data Storage migration is yet another partial modernization strategy to migrate your data storage to a new database, and/or consolidate your databases into a single unified database.