In JoSAA counselling if they allotted a seat to me ,it may further changes by them?
Well, if you freeze a seat once it has been alloted to you, then you have a confirmed seat which will not change since you would not participate in any furthur rounds of counselling.
However, if you choose the float/slide option then you can get your seat upgraded as per your choice list and then the previously alloted seat will change.