In theory, I know this. I've always kind of wanted to run something where I pit players against creatures that have the exact same game mechanic stats as modrons, but change the name and describe them as looking completely different than the modrons of the books. But even if that did work, I've changed them from really being modrons at that point. I've just found a really easy way to get rid of them, is all.
I don't see the need. I'm departing here to a very very small degree from what is found in the books. About the only difference is I explicitly call out the arms and legs as being robotic like extendable appendages of the modrons, rather like R2-D2, and I'm highlighting the robotic quality highlighted in 2e. So if you encounter monodrones at rest, they'll be piled in pyramids like cannon balls (often with a quadron or tridrone supervisor at their center). They'll roll around, extend legs and arms as needed, etc. An encounter with monodrones on their home plane might be something like:
"In front of you is a pile of spherical steel black objects, each about 3' in diameter, and piled in a tetrahedron 4 to a side. The objects aren't simple spheres however, as closely examining them shows incisions and groves of various sorts in their forms, forming a complex pattern on their surface."
Followed by something like...
"The pile of spheres elegantly begins to slide apart, so precisely it is almost noiseless, as each sphere begins rolling and turning along with its neighbor and forming up in ranks on the floor these roll toward you in a tide of steel gray spheres. At the center of the tetrahedron, you can now see that the balls concealed a solid tetrahedron, 6' on a side which rests on the ground."
Followed by something like...
"As the spheres get about 15' from you, they begin to extend spindly limbs so that they roll to what can now be only called feet. Simultaneously, as a cordinated action, a sharp point extrudes from one side of the sphere and lengthens on metal rod very quickly like a needle being pushed through cloth by some unseen sewer. The spear is followed by an arm, and within moments the mass of balls is transformed into a phalanx. At the same time, a metalic eyelid on each sphere opens with a click revealing a crystal ball like eye which glows with a dim blue light. In a low droning voice, the phalanx chants in unison, "The One Knows. The One Is. All are One, and The One is All." Likewise, the tetrahedron now sprouts limbs and flicks open eyes on each of its sides, and from the passages and ramps leading into the room, more spheres are rolling into place. The entire chamber echoes with a hum and drone."
Have I changed them from being modrons?
How would you have them look? One of the advantages of the original modron design, whether optimal or not (mostly I'm only unhappy with the pentadrones, whose appearance doesn't seem to fit with either the drones or the heirarchs, or even meet either halfway), is you are never going to mistake them for having a human outlook.