No. Stall speed is a function of the wing, not the prop. The prop can change the landing characteristics of a plane, but only in some ways. If the plane is still flying well above stall speed with the engine idling, a lower pitch prop can let the plane slow down a bit more. It'll sacrifice some top-end speed as the trade off.

In your case the plane is already at its stall speed, right? You can't reduce that by changing the prop. I've got an Ultrastick 40, and I can't imagine it getting much slower on landings. It's got a very low stall speed and will land at a fast walk. How heavy is yours? Lowering the weight is the best way to lower the stall speed. Mine is stock, with no added weights but an Irvine .53 that probably weighs just a hair more than your .46fx.

I'd try a 12x4 prop instead of a 12x5, and a 12x6 is going to be a bit much for your engine. I don't care too much about top speed either, and I've found a 12x4 on my 46fx gives me great flight characteristics on a variety of planes.

Lastly, are you sure you're flying your Ultrastick down to stall speed? I've got a friend who for a long time would land his Big Stick hot, and I mean hot. He always said he was worrying about stalling it on landing. He finally played around several mistakes high and realized he was nowhere near stalling it on landing, and now floats it in nice and slow... most of the time.