I believe Law can cut it without being in contact with the Kairoseki itself. Kairoseki has the same effect as the sea to a DF user and only drains their powers,
Not that it has some effect on the result of their powers if they use it somehow (like Luffy did underwater, though he used Haki but Haki didn't protect his powers from being drained). Take for example,if you think that law can't cut it because he's a DF user then he can,,, he can, it's just like Fujitora pulling down a meteor on a Kairoseki something and destroying it even though he is using his DF powers.. If you think he can't cut it because of its hardness then no, Law can cut it without being in contact with it, there is nothing that contradicts it, he can remodel anything in his room.
One more thing I'd like to point out.
-Law changed the sea stone shackles with normal ones(when he and Luffy were caught), because he couldn't have been able to use his powers properly then and cut it. He was able to do that but then in that condition (in contact Kairoseki) he couldn't have done it.
I didn't understand this part. Explain again, please.
I just said that Law's DF can't just bypas anything because according to Doflamingo a strong enough Haki, compared to Law's cutting attack, won't get cut by Law.