Just got Waterloo; so far so good, Austerlitz Napoleons greatest victory was my goto Napoleonic warfare until this came out

but I digress....
I would like to do a small sandbox game with all three "branches " CAN/INF, ARTY but it seems to have all three at once you must control a very large formation. Is there a way to customize a "smaller and manageable" OOB to have for example 1 BN of Cavalry, 1 battalion of arty and perhaps 3-4 infantry?
Appreciate the help!