Geraniums, like many plants, grow into a "flowering mode" in which the branch just produces flowers, and does not become a bushy plant. So, yes, you can pinch the main stem which will make the plant bushier. At this point you would take light pinch. However, if you let it grow higher, at a later time you can take a heavier pinch, say down to the point it is now, which at this point will become a cutting. Remove most of the leaves, and apply a rooting medium. I would use sterile "soil" that you sterilize yourself to help prevent the plant from pathogens in the soil from killing it---an easy task that will prevent your losing cuttings. HERE'S HOPING YOU ARE SUCCESSFUL.