I've found that renaming the file doesn't break the license at all. Now, opening the file and making a change surely will.If you transmit the file with a different extension, won't it corrupt it? I'm not sure. Just I've guessed with the same behavior while uploading a file to forum with a different extension. But, probably, I'm wrong.
Well, just do this simple test. Take an image file, such as a jpg. rename it to .dat. Then, rename it back to .jpg and try to open it.
It should work just fine.
The problem is when you try to rename a file, open it up and change something. Once saved, it's screwed. If you don't touch anything but the extension, it shouldn't do any harm.
I've done this with exe's as well, since Outlook and most internet providers will prevent exe's and other files from being sent in emails. If I had to get a small exe over to someone quickly, I'd just rename it to ._xe or something like that and send it with instructions to the recipient to change it back to an .exe before trying to run it. Always worked in the past...