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Not really. But I advice that you should refuse it most of the time (unless you have extra kokujins to give away), because if you have promised land to more than one character and give land to one, it automatically breaks the other promises. Refusing to give land always makes your vassal to dislike you, but the opinion hit is bigger if you first promise and then don't give the land.
 
Also the opinion hit doesn't stack so if you refuse the same guy 10000x you'll get the opinion hit only once.

I should play a round of this again sometime while I wait for Art of War :D