The Information Bulletin is not clear about this. But since choice filling has to be done just once before the first round. you cannot change preferences in the subsequent rounds. Meaning, if you have selected your preferences before Round 1 of Maharashtra State NEET Counselling, the same preferences will be used for Round 2 and mop up round. Based on your options once you are allotted a seat, the same colleges and preferences will be considered for Round 2 and Mop Up round. So you cannot change your preferences in Mop Up Round.