Not exactley. You can sleev and port or even buy a sleeve with a relatively different port layout all together. The problem with putting a big bore sleeves in stoccylinders is that they choke off the already small transfer ports. Then you are trying to fill a bigger bore with less air/fuel mixture flow.
A "big bore" or aftermarket cylinder is typically the better option. There are quite a few different cylinders available now with a few companies offering different port layouts that accommodate different riding from Trails, Dunes , or Drag Racing. They typically have far better port layouts and larger transfers or even more then stock amount of ports. This allows far more ability for a cylinder to pump more air and fuel mixture which in turn makes more power. We are to an age where a lower port time cylinder can create almost the same kind of horse power as a high strung drag motor, but just a bit sooner in the RPM's.