G’day & welcome Scott!
I presume you’re referring to an external wall (part of the perimeter of the building). Please provide more details if that’s not the case.
Wall location is determined by the centreline of the core. If you change the width of the core wall from 70 to 90, the cavity & veneer will be pushed outwards by 10mm. Just rt-click on the wall, select the MOVE option & pick a point, type half the difference in wall width in Commander (in this case 10), with ORTHO=ON drag your cursor perpendicular to the wall toward the interior of the building. Press ENTER. The external face of the venner will be back where it started.
hth
Merv