Migration

Migration is the project where nothing should visibly change for the customer and everything changes underneath. Products, orders, customer accounts, URLs and search rankings all have to arrive intact.
Steel Racing moved to CS-Cart and was redesigned in the same cycle. Elit came across as a catalog for medical professionals and had to keep its B2B pricing logic through the move. Podguznikoff carried several city storefronts across at once. Stomdevice moved a dental equipment catalog where product data is unforgiving of import errors.
The part clients underestimate is URL mapping. Every old address needs a destination, and a migration that skips this quietly loses the traffic the store spent years earning. We build the redirect map before the first product is exported, and verify it after launch rather than assuming it worked.
If your current platform has stopped fitting the business, see migration to CS-Cart.