Well, it's complicated but I can explain how to do it. You might mess it up a few times because it's tricky. Make a new image at the size you want and fill it with clouds. On your original image and take the clouds layer from that, copy it, and paste it into the new document. You should see a clearly defined edge between the two clouds layers. Now take your "base" layer from the original and copy that into the new document - this lets you know where to stop editing or airbrushing. Now take an eraser with an airbrush tip and low opacity and erase the edge. I mean low opacity, like 5% or less. Flip back and forth between black and white colors and airbrush places where the eraser doesn't seem to work well. What you want to end up with is something where the "new" ocean is much darker and the areas around the coast are lighter and the hard edge is blended out into oblivion. If you have a tablet you can have much greater control of erasing and airbrushing. Once you have this then delete the "base" layer from the new document and merge the two cloud layers together. Now do the steps in the tut for ocean colors and then copy everything from the original document into the new one (ctrl-click a layer in the original, edit - copy then edit - paste - this will keep things centered so they should all line up properly in the new document). All you have to do now is save the document as something like "continent tweaked" or something like that.