if any student can change their course mode after completing 2 year of 3 years course

you have to leave your current course this is possible in some courses in which there are so many branches like engineering , you have to start again from ist year if you leave your course

Student may choose private exam in 3rd year after completing 2 years with regular and they will get a private or non regular degree only due to one year. but you cant go for regular after completing 2 years with non regular.