I wrote my rebuttal to the three reviews but I went 81 words over the 500 word limit and it is bolded next to the submit level. Is it bad if I submit with the surplus of words or will I not be penalized?
Yes, you will be penalized. One of the difficulties of rebuttals is saying everything you want to say in a manner that is condensed and clear within the word limit.
So is the word limit 400 or 500?
The word count must be between 300 and 500. The word limit is 500.