[Update: This 30 July 2017 post rendered this post redundant.]
In this 2015 post I consider Nothing in this agreement gives X the right to [do something].
Now let’s consider Nothing in this agreement prevents X from [doing something].
We have to ask the age-old question: what category of contract language is this? Is it language of discretion? In other words, how about saying instead X may [do something]? I wouldn’t do that: it suggests that X is being granted permission under the contract, whereas the point is that nothing in the contract interferes with X doing whatever it it.
I say it’s language of declaration: Y acknowledges that nothing in this agreement prevents X from [doing something].