Go into Chomps 4 (Inside) and copy and paste Chomps 4 folder into:
Program Files -- Steam -- steam apps -- Age of Empires III -- bin -- Campaign
Copy and paste homecitySPCAct3 into
Program Files -- Steam -- steam apps -- Age of Empires III -- bin -- data
The American home cities require the new cards in homecitySPCAct3, so use it!
Then from the editor select a civilization, then Reset HC and then press Set HC, and select Chomps 4, then 2015 Du, 2016 Am, 2017 Ot, 2018 Ru, or 2019 Am. The last Am has five decks; the rest have four decks to choose from.
Thus: Campaign -> HCs -> Chomps 4 -> File
Each homecity has Sea, Field Army, Cavalry and Frontier decks in it. 2019 Am also has an Economy Deck.
The first time you select to load a homecity, it will fail to load, just as with music files or with AI loader standard. If you press OK afterwards, then load your scenario and Set HC again, it will work. Note that Computers cannot use custom decks, unless you enable it from the AIHeader or AIMain.xs.