Modifier for wall thickness

Hi there

I saw I could do this so put a modifier on one of my parts to increase wall thickness in this area (where a screw will go)

Seemed simple enough picked the modifier part and increased wall thickness. However when sliced it offers no evidence of this?

I have set o printing it so will see what it does but would have thought the slicer would show that change?

Yes, usually, it prints as sliced. If the feature you are looking for is not visible in the slicers preview, you are better off checking your modifier for correct assembly with the object to be modified and its individual settings.