No, you can't paint light bulbs - they get hot (well, except LEDs) and will burn off the paint. And you won't get the effect you want anyway, as painting the top half of the floodlamp bulb won't cause the top half of the light output to disappear.

Instead, replace your recessed can with one that takes an aimable MR16 low-voltage bulb (which can typically be aimed up to 35 degrees off center, sometimes more) and use a slotted trim like the one linked to below. They are available from many manufacturers and in all the common can sizes (6", 5", 4", 3") and are usually white. The reflector bulb is tiny and hidden above ceiling level. Google " recessed slotted trim 6" " or whatever size you need. MR16 bulbs are available in different wattages and in about 8 different beam spreads so you can get exactly the size you need, and they focus light very well (they need special low-voltage dimmers though; if you need to use standard incandescent dimmers, find a can that takes GU10 or PAR16 bulbs). Or you can get a "wall washer" trim (half open) that uses a standard light bulb, but these put out a more vague light pattern.

Here is a link that might be useful: Slotted Trim

If you really want to, you could try using paint intended for high temperature environments. However, you will need to paint the bulb after it has been installed. Overall, it probably won't work - could shorten the lifespan of the bulb, paint results not quite satisfactory given the amount of manual effort put in. In addition, high temperature paint is not cheap.

The best solution would be to try what lee676 suggested.