Baking scatterers is not a must-do if not needed. You can easily let your moss "dynamic" and combine the moss scatterer with the underlying rock. So you keep the control on the moss.
You can tweak the original scatter, then bake, then re-tweak the original, then re-bake etc...
In this way, you can make a bunch of variations in no time. Keep in mind that when you bake you lose the procedural behavior of your setup.
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In this setup, you just have to drop/clone stamp objects in the "scene/Rocks" context and moss will appear automatically on your object.
I explain the setup. In the Rocks context is a dynamic group that gathers objects automatically with a dynamic rule. This group is added to a Combiner. So each time you add an object in the Rocks context the combiner gets updated. Then I create a point cloud on this combiner, set to density. So regardless of the number of "Rocks" the point cloud stays homogenous. Then I use a scatter with this point cloud as support and Moss as geometry.
So Each time I add an object in the Rocks context, the group gathers it, the combiner gets updated, then the point cloud gets updated as well and so do the moss scatterer. Finally I used a gradient in Slope mode to decimate the point that pops under the rocks > Full procedural

Cheers