No matter if the units are from RTR 6 or reskinned, or new models or whatever, the guy's initial question was how to make them available in Custom battles.
to do that, I think all you need to do, is open "Rome Total War\FOE\Data\descr_sm_factions.txt"
And change for the faction "slavs" (which is Macedon) "Custom_battle_availabilty no" to yes
I must warn you though, that we have not tested or balanced this...
Btw, I also think you might want to do the same for the faction "greek_cities".... No guarantees on the workings of that though, but well... maybe you'll like it
