Keep what already works
Not every part of a legacy system needs replacing. Identify stable capabilities that the business depends on and protect them while the surrounding system changes.
Create clear seams
APIs and adapters let new components sit beside old ones. They make it possible to replace one capability at a time without a risky all-at-once cut-over.
Move one measurable workflow at a time
Choose a workflow with a visible outcome, move it, and measure the result. Each successful step builds confidence and funding for the next.
Retire with evidence
Switch off old components only after usage data, reconciliation checks and a tested rollback plan show that it is safe to do so.