Set the thickness and build-up note on a cloned thicker board
When you clone a board to make a thicker one, record the real thickness in the Thickness field and any build-up note in the brackets field.
When creating a thicker board from an existing one, the Thickness field on the cloned board's properties must hold the real thickness value.
Any note about how the board is built up (for example that it is made of two thinner layers) can be recorded in the brackets field instead.