With the Cut Geometry tool, you can pick and choose which geometry gets cut and which does not, regardless of when you created the geometry.
When you create a void, it affects only existing geometry. In this case, you can use the Cut Geometry tool to cause the void to cut solids that are created after the void.
You typically cut geometry with voids. However, you can cut certain models with solids. These models include conceptual masses and model family instances. See Cut Geometry with a Solid Form.
You cannot cut system families, detail families, and profile families with solids.
Video: Working with Voids
To cut geometry with voids
Notice the cursor changes shape.
Revit cuts the selected geometry.
You can cut objects in a project when a family with unattached voids is loaded.
Objects that can be cut include: Walls, Floors, Roofs, Ceilings, and Structural Framing, Structural Columns, Structural Foundations, Casework, Furniture, Specialty Equipment, and Generic Models.
For example, when placing a sink in a project, the void defined as part of the sink family can cut a countertop. When placing a recessed light fixture in a project, the void defined as part of the light fixture family can cut the mounting surface.
To cut objects in a project using voids in the family