In the AD&D 2e book The Planewalker's Handbook, p. 76, it says this about Rogue Modrons (italic emphasis in the original, bold emphasis mine):
...most folks can't tell a rogue modron from a "normal" one just by listening to it talk about the multiverse. It still is an extremely ordered being, with law at the center of all of its thoughts and in-grained in the way it feels, acts, and reacts.
Rogue modrons stand exactly 6 feet tall, with cubelike bodies similar to those of quadrone modrons. The cubes are 3 feet on each face, adorned with two thin 3-foot-long legs, two 3-foot-long arms, and a pair of small, vestigial (nonoperational) wings on their backs. A vaguely anthropomorphic face can be found on the front cube face.
So, in short, even a rogue modron is "an extremely ordered being", which I take to mean "is always lawful" (probably lawful neutral, like "normal" modron), and they apparently always have "cubelike bodies" like a quadrone.
A monodrone that doesn't want to rejoin its fellows is a rogue modron, made so by the chaotic energies suffusing the Underdark. This rogue monodrone gladly joins the party, saying "Down with Primus!" in its own language over and over. Its alignment is chaotic neutral, and it can only follow one simple task at a time.
So there seems to be a contradiction when comparing information between editions. Is there any further evidence to support that the restrictions placed on rogue modron from previous editions no longer applies to 5e?
Or in other words, can I really have a chaotic rogue monodrone as opposed to only being allowed a lawful rogue quadrone in 5e?