Of course you're dealing with your local licensing authority, but they'll all have a rule substantially the same as the model rule cited.

California's state bar even has a formal opinion calling out this or similar behavior:

"Had Seller’s Attorney intentionally created a defective “redline” to surreptitiously conceal the change to the covenant not to compete, his conduct would constitute deceit, active concealment and possibly fraud, in violation of Seller’s Attorney’s ethical obligations."

[https://www.calbar.ca.gov/Portals/0/documents/ethics/Opinion...]