Is it necessary to have the deck surface changed to run cometic head gaskets on the new world blocks?

Yes, although you might get by with some re-torquing and some Bars Stop Leak.
I know the as delivered deck was pretty square and flat, looked good. I had to mill anyway to get desired compression and deck height.

You can get a seal even with a blanchard cut finish with Cometics if you coat them with a hi-temp sealer and retorque after a few heat cycles.We use Permatex Copper Seal.

Mine didn't Seal well the first year. The cylinders liners in the World block were above the deck surface and prevented the gaskets (Cometics) from sealing on the block so I had water in the oil all year. They sealed just fine around the combustion chambers.

This year I went to B1 heads so that meant a complete tear down on the motor. After running the block all last year the liners got seated. My machinist just needed to take a skim cut on the deck surface to straighten everything up. He put it back together with the old Cometics from last year and some copper coat. No more water leakage.