Go in the Models folder and find the file called "m_norsebarracks_melee.dds", then rename it "m_greek_catapultworkshop.dds". If it asks you to delete the previous file, say yes.
You do the same as with the norse barracks but you copy paste s_greenwarriord, name the new 1 s_greekarcherd and replace the original s_greekarcherd with the copy. If that makes sence :laugh2