what if a file extension change?

1. Avamar can exclude files by its extension ex: mp3

2. If I change an mp3 ext to txt, then avamar will backup that file even i set an exclusion rule for mp3, cause Avamar dont check content of information.

Question?:

Does anyone from this forum knows about a software that scans the file content or check if the extension of the file is what it is.

I have a client that need to exclude mp3 files from backups, but users change file extensions so Avamar will backup the mp3 files with different extension

thanks for your help