Hi Sethi,
Can we use one value multiple times in drag and drop?
This depends on the question. In the question, they will tell you to something like "You can use one item for several slots" or you cannot.
Also, if we have dropped wrong value in one box and later on realise it, how can we change it? Would just dropping in the correct value over the wrong value overwrite it?
You can remove the old value by dragging it away. And then you can place a new item to the slot.
If you need more experiences on drag and drop questions on the exam, I recommend you to try Devaka's
examlab simulator to get more experiences on drag and drops. Because that simulator software gives you the Sun exam feelings.
Good luck for your exam