So the AP2 OEM rear and front wheels have 65mm and 55mm offsets. If I replace that with a set of aftermarket wheels with 55mm and 45mm offsets, is the visual effect the same as adding a 10mm spacer to the OEM wheels?

 

Yes as long as the wheel widths are the same.

 

If what you mean by visual effect is the position of the tire/wheel outer edge in reference to the fender/wheel well, (ie. te extent of poke or indentation, or flushness), I agree, yes. But there are other characteristics of the wheel that impact the visual effect. For example, the extent of the concave appearance has a big impact on overall visual effect. The aftermarket wheel with the specs you mention might appear more concave than the oem wheel with a spacer. Using a spacer does not change the concave appearance (or lack thereof) of the OEM wheel. Aftermarket wheels may look a lot different in that regard. It depends on the specific design.