WM6.1 Renaming files
 

So, I have an HTC Touch with WM6.1. I have a few files I'd like to rename. Only problem is I want to rename the extension, you know the .3 part.

Can't figure out how. Is it just not possible with the default software? I ask that because I need to send these files to a client and the stupid filters block them (certification files) when they are .cer files.