Keen: Modding

Inkscape, as well as many other graphics programs let you group several objects together with a sub z-order inside the group (which can also contain groups with another level of z-ordering. it is not a difficult thing to deal with since ctrl+g will group all the selected object and shift+ctrl+g will...

Probably the easiest way to do it is to split object D (or any of them, actually) into two separate objects that are seamless and thus appear as a single object. Although if any of the other objects were to ever intersect the seam, then you would have a problem.

could this be used to modify all of keen's sprites based on the level?