I released a video many years ago on how to install mods via Steam for Empire at War and Forces of Corruption. With the release of the new patch bringing back multiplayer and whatnot I thought I'd give the game another go and try out some mods too!
I could not install them for the life of me from the steam workshop (game just kept crashing), by my old option or in the game via the "mods" option where people said it'd close the game then restart with the mod. So I went for a final push and created shortcuts instead and used the information you would put into the launch options on Steam but into the "target" box of your shortcut file of the main .exe for the game.
Watch the video below, this was the final straw before I just played online and a few campaigns and let the game rest. Fortunately it worked for me and I can enjoy some of the great mods the community has made!