client old offline install overrides current system version?

Hi, I'm making an installer for my app which uses a flash app that eventually runs an unity3d app. This sofware is supposed to be installed offline and as simple as it can be.

I'm currently running it silent (UnityWebPlayer.exe /s).

My question is, would an offline silent install of an olver version of unity client replace the current newer version in the system?

Ie. I have installed version 3 of unity3d on a computer, if I install version 2 silently, would 3 overrides 2? or what happens? does it throw an error or something?

Remember all this is offline mode. Thanks in advance.