Need to DOWNGRADE from 12.1.2100.2093 to 12.1.2015.2015

When I try to install 12.1.2015.2015 onto an XP machine that already has 12.1.2100.2093 I get a message "A newer version is already installed"

I know that. I want to install the older one.

Anyone have any suggestions? This needs to be able to be automated since I have about 350 XP machines with the WRONG version of AV on them (broken teefer2.sys screws up SMB. ) and ABSOLUTELY need to install the older version.

Thanks.