This is not just used to evade censorship, but also humorously. E.g. returnees from overseas 海归 (hǎiguī) are frequently called sea turtles 海龟 (hǎiguī). In that case, even the tones match.
By the way, I’m not a linguist and I just completely made up that usage of “atonal homophone”. Could an actual linguist chime in and tell us what’s the correct way to describe a “homophone” that doesn’t match in tone, in the context of a tonal language like Chinese?