A better strategy is to first move a small part of it out of the system. And not go for a complete rewrite. And then make sure the old system can work as a proxy for the new system, or vice versa.
When both can be used simultaneously you can now gradually move from one to the other, or revert back as needed.
It reduces risk of failure but can end up costing more in the end. It's like doing a home renovation piece by piece rather than all at once: if you have the capital upfront and an experienced professional, doing the whole reno at once will be cheaper.
When both can be used simultaneously you can now gradually move from one to the other, or revert back as needed.
This is what I followed.