FSUIPC Key Assignments

Here's another little thing I discovered about FS9. When I am flying and want to Cancel IFR, I am always told, "Frequency change approved." In other words, set Transponder to 1200 for VFR. I wanted to assign a key through FSUIPC (v. 350). I tried putting 1200 in the Parameters box but it didn't work. I tried all kinds of numbers but nothing worked. Then I just tried 6666, I don't know why, but it put 1202 in my transponder. So, I went back in and changed the parameter to 6664. That did it! Go figure. But, now, when I want to set Transponder to 1200, I just type Shift-x. Neat.