It is an interesting approach to baiting people. Bowdlerization and other forms of censorship could be considered "opposites" to this. I tend to prefer the contrast with the idea of minced oaths:
A minced oath (also pseudo-profanity) is an expression based on a profanity or a taboo term that has been altered to reduce the objectionable characteristics. ... The most common methods of forming a minced oath are rhyme and alliteration.
Meanwhile it shares many similarities with eggcorn:
An eggcorn is an idiosyncratic substitution of a word or phrase for a word or words that sound similar or identical in the speaker's dialect. The new phrase introduces a meaning that is different from the original, but plausible in the same context, such as "old-timers' disease" for "Alzheimer's disease". ... Eggcorns often involve replacing an unfamiliar, archaic, or obscure word with a more common or modern word
The user seems to be attempting to create a malicious eggcorn in the reader's mind, replacing an archaic term with a more modern (and offensive) one. Indeed, seeing as the original word was primarily negative, a racial slur could introduce a meaning "different from the original, but plausible in the same context."
There have been numerous public controversies over this particular word pair. (Controversies about the word "niggardly")
Ultimately, though, I think the word to describe this behavior best might just be "trolling."