I was forced to install this. The first time I tried not installing that and got some message about a missing file whenever I tried to run this game. So I reran the installer and let is install 9.0c and the game worked.
Does this overwrite my DirectX 11, or whatever it is now, files?
No it doesn't, DirectX 10 and 11 are updated through Windows Update IIRC and don't interfere with older DirectX versions. DirectX 9 setup OTOH updates you to the latest version 9 and older versions because 9 is backwards compatible with older versions