Birger T Is this how you imagined modular feet? With the right length small screws and the right thickness feet the hole would not have to come all the way through the wrap-around part.
I just split the foot depth in half here for a quick sketch, but it might be better to have a thinner section on the leg servo section, just enough to hold the head, and a thicker section for the screw to grip on whatever design provides the toes/flippers/claws/etc.