Yes, Mock/dummy allotment list has been released. Now, you can change the position of colleges, wait for the original merit list of allotment , again choice filling will start for second round. .
In the duration of choice filling, you can change or delete your college, or whatever you want, since colleges will be locked only when the time period is over.
Hardly, there will be 2-3 days for each merit list, so there will be only 2-3 days for the choice filling for upcoming rounds.