Resize cabinet end panel at design panel level, not admin portal
Change a cabinet end panel's depth in the design phase at the panel level so the change applies only to the cabinet you are working on.
To change the depth of a cabinet end panel (for example to extend it by 20mm at the back), make the change in the design phase at the panel level rather than in the admin portal.
Editing it in the admin portal would apply the change to every cabinet, whereas end panels are typically only needed for corner cabinets.