It should work, although some things may not appear correctly. One of the main problems you will have is the fact that OS 4.6 had a media app while 5.0 uses a media folder with separate apps. With a 4.6 theme, you will get a media icon that won't do anything when clicked, and you will have the separate icons (pictures, videos, ringtones, etc.) that won't be skinned to the particular theme.
As stated above, some sites may refund your money, and they also may just let you switch it to the correct OS, provided there is one available.
It was the animated arena theme...it worked. havent checked the media folder yet. But the rest seems fine and the animation is cool! Hope its ok hehe...
edit: actually the media folder seems ok as well^^