The more your word count differs from the 'average' for that genre the more likely that you will have problems selling it.
The farther away you are from their target (which is often a range not an exact number) the worse your chances.
So if you are going to deviate you had better have a much better plot and a much better written novel. Especially if you are previously unpublished.
And when they do list a range for wordcount you should be in that range and not higher/lower.
There is a reason for word counts by agents and that is because they have to sell your mss to a publisher. And they know what makes it most likely to make the sale for you.
So to answer your question in the OP, yes, if your mss is much much more than the typical book you have pretty much ensured that no agent will take that mss and no publisher will buy it.