Iso thickness areas modification after the areas have been created.

[l3obAero]

I've been working with the 'Grid' method on an aircraft composite skin. I see that once the 'Iso-Thickness Areas' are created using either complete stacking of selection of groups, the selections made are not modifiable/under-intensified after the fact. Example: I made the Iso-Thickness areas from a stackup selection of groups, I added some 'non-structural' plies afterwards, now I see that I cannot go back and Add the added group to the iso-thickness areas; it looks like once selection is made, you're locked in. Does anyone know how to modifiy or force catia to re-calculate the selections of groups to add new groups, switch from complete to selection of group, or switch from selection of groups to complete, after the areas have been made?