I have got a component which is a wall. I want to add different cutting to different walls. However, I do not want to make walls unique, since I want to be able to resize walls in the future.
Windows and doors use cutting areas to cut into wall elements, and those windows and doors are saved as components. They cut into live geometry, not other components. If you declare a given component "unique", you can then make edits to it which do not reflect on other similar but not the same components, and if you then copy that component, changes you make to one will impact all others of that type.
You CAN cut components which are solid (watertight) using the SketchUp solid tools (Booleans) and THAT would work fine - but might be a bit... labour intensive - but I think it's your best bet given the constraints you've mentioned.