If you make it worse, it's cheating and getting caught. Sometimes you might luck into a correct usage of a word, but like using a LLM, the nuance of that word choice is not part of your thinking, so it's a loss of information that you did to try to appear to be a better writer.
Does learning/using new words make you a worse writer?
The handful of times I've used a thesaurus is usually 'for aesthetics', in that the word/phrase I have in mind clashes with the flow of the text. I know what I want to say, and I know how I can say it, but I _also_ know that I can jostle the wording around so that the rhythm doesn't deteriorate.