You talking about a drop-in cooktop verses a 'standard' range?
A cooktop may just have a cabinet beneath it, and if you measure the opening, you may just have to remove the screws,cut the counter, and slide the cabinet out. You could finish the edges of the counter while it was out, then adjust and maybe add a connector for the new stove, and slide it in. It would likely be a little messier if it is a gas range or dual fuel.
IOW, it may not be that big of a deal...measure the cabinetry beneath what you have now to see if it is a standard size. They're usually 30", and go in 6" increments if you want something bigger and fancier.