Me trying to understand NUST merit list: 🫩

Does anyone know that if we get our 2nd or 3rd preference in first merit list, and we pay the fees and apply for hostel... And then in the next merit lists we can be upgraded to our 1st preference if the marks allow BUT what I don't understand is that if I get into an engineering program in my first list And then I pay the fees does that mean that I cannot switch to a computing program in the next lists? Cuz I think I might get into electrical eng in first merit list but I wanna go for CS And I won't get into CE until the 3rd or 4th list probably So can I just pay the fees for electrical eng in first list and automatically be upgraded to CS later on OR THAT ONLY HAPPENS IF I PAY THE FEES FOR A COMPUTING PROGRAM?????