Re: setting a song to 2/4 - at the first bar of the song, hit F5 (the bar settings window) and enter 2 for the number of beats per bar. From then on your song should be in 2/4 until you change it back to 4/4 or 3/4 with the F5 window. As you may have noticed, the beats per bar in the Bar Settings window will be 0 when you open it (unless you have already changed that bar - the default is 4/4 so I have always thought it should say 4 but it is a small issue), so if you change it at some point you will need to type in the 4 to get back to 4/4.
Good luck.