You could do like Dan suggested. I'm unfamiliar off-hand if you could modify what you already have into multiple regions without ruining the outer boundary.
How I just did this (to create snow districts) within our County boundary, was created a new Feature Layer (I'm using Pro), but you could do a shapefile in ArcMap. Then I drew in rough boundaries for those new districts within the county boundary. Then when the rough draft was done, I went back in and use the "Reshape" tool which helps to match the county boundary so you don't have to do all of that manually.
There may be an easier way, but that's what I did.
Another thought, you may be able to take the copy like Dan suggested and use the Split tool to roughly slice the county into those new regions, then go ahead and modify each geometry manually from there. That way you don't have to use the reshape tool to match the boundary.