Change what kind of type file downloads as

Changing the extension of a file doesn't change its content. So, you can change extensions back and forth to whatever you want without harming the file content.

To see what type of file it is, you can open it up in VLC or Media Player Classic or whatever and look at the media infromation and it'll tell you want it is. Or, you can open the file in a text editor or hex editor and look to see what header it is. You can look up on the net what the headers look like for raw file types and contains so you know what to look for. Mp3s with ID3 tags for example will usually have ID3 at the start of the file (but could be at the end). You might also see the encoder listed somewhere. "Lame" for example. Besides that, it's more complicated. Other file types are easier. If it's an mp4/m4a file, if you open it with a hex editor or text editor, you'll see the headers right away.

You could also use the Network tab in Opera's Developer tools (disable cache, refresh and try the download again) to examine the headers sent for the file. If it's audio/mpeg for example, it could be an mp3.

Your example filenames seem really weird though.