Copy boundary
Add > Boundary > "Around Selected"
You will set the offset as a positive or negative number depending on if you want the boundary to be inset or offset.
For example, if I want an inset boundary that's 10 feet smaller than the original geometry, so I've set the Offset as -10 ft.
In the example below you will see a property line and we need to add a setback of 30 feet. You will clone this boundary with an offset of -30 ft because you are making the new boundary inset. When generating layout you will select the cloned boundary and be sure the original one is deselected when selecting area.
Also in this example we have a body of water in the bottom right corner that we want to offset. You will clone this boundary using an offset of +30 ft because you are making the new boundary offset. Make cloned boundary your new exclusion zone, leave existing as is.
The Final Result:
