Hotbutton, If the concept is four characters all conforming to the size of a circle and geometrically repeating elements of that circle, yeah, the concept is compromised by any alternations that lie outside that concept.
However, a less geometric and humanist interpretation of the concept might allow for some consistently applied tweaks and refinements that provide visual clues and better balance while retaining the overall rhythm of the geometric shapes that it’s based upon.
Trying to achieve a middle ground of keeping as much of the concept while making it more legible is, perhaps, like you mentioned, a recipe for some not-so-good-looking glyphs. Personally, I’d be inclined to abandon a strict adherence to the concept and concentrate, instead, on preserving the colors, flavor and rhythm of the whole thing while paying more attention to designing some glyphs that could stand on their own as aesthetically interesting.
Heading down that road might lead to something like Milton Glaser’s Baby Teeth typeface, below.