NO! (in a word). The whole restraint in the knapsack problem is that there is NO way to somehow "trim" an item that's just a little too large, down to the ideal size, or to increase the capacity of the knapsack to accomodate the items we'd like it to ideally, hold.
It seems to me that if the "knapsack" can somehow have a dynamic capacity - well, maybe that's NOT a knapsack problem, after all. Another name to describe that type of problem would certainly cut down on misunderstandings. adak