I beleive yes. But not sure. I did a few mods with empire off steam and I had to search through the steam folder and find the 'Steamapps' folder. Inside that go to 'common' folder. The the Game name folder (I assume its Rome:Total war or soemthing...figure this bit out yourself). Then do your thing in there. I don't have rome via steam so can't tell you anymore than this but looking at the games I do have I can see that this is where all their data seems to be kept. Maybe if you direct the installer that comes with the mod to this folder you will be fine...maybe not. Try it out and let me know.

If it doesn't work you might need to 'verify cache' or whatever via steam to fix any problems you might have caused. Good luck dude.