Don't try to rewrite the whole system in one go. Move incrementally. You can start by creating your own UI that performs most common functions and uses existing

Don't try to rewrite the whole system in one go. Move incrementally. You can start by creating your own UI that performs most common functions and uses existing system as a backend. This way you can automate what you need and work around bug. If it goes well then later you can gradually move to your own backend.