It's not a mod but a beta of the next official patch. And the checksum is in the thread title.
You should only ever install betas over a copy of your game, not over the real installation. So copy your whole Rome directory structure to somewhere new like c:\games\rome-beta\ . Then you have to download and extract the beta file, say to your desktop or MyDocuments directory. Then drag'n'drop the whole beta directory structure over your /rome-beta/ copy so that each new file and directory overwrites the older ones. Run it by manually double-clicking on rome.exe in that new folder.
You should only ever install betas over a copy of your game, not over the real installation. So copy your whole Rome directory structure to somewhere new like c:\games\rome-beta\ . Then you have to download and extract the beta file, say to your desktop or MyDocuments directory. Then drag'n'drop the whole beta directory structure over your /rome-beta/ copy so that each new file and directory overwrites the older ones. Run it by manually double-clicking on rome.exe in that new folder.