Lighting "always" needs to be rebuilt

So question on this, you note that foliage with too many instances for them to all fit into one lightmap. I don’t see this anywhere in documentation but how do you go about making more instance clusters of foliage. So for example we have a forest scene and all the foliage is in one group but there are not layers to foliage correct? When I am in Foliage select mode there is only the option to “select all”. How do I get instances in different clusters? I am getting Unlit errors after lighting only on my two foliage levels an none of the others.