If i'm right you can't migrate before atleast 1year in NUST as per policy, so you'll have to wait for 1 year in Nust if you want to migrate/change subject... and that too depends upon:
1)Your GPA, grades etc
2)Availability of seats in the respective department
credit hours are transferred from one engineering department to another.........
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You can apply only after 1 year in Nust and before the final year....
Changing the schools is REALLY REALLY difficult,and requires
1. a really good gpa
2. Availability of a vacancy
a girl transfered from EME EE to SEECS EE,her gpa was 3.9
BUT,changing majors in the same school is comparitevily easier,any thing above 3.5+ will really really strengthen your chances for it,otherwise even a 3.3 or in SOME cases, a gpa of 3 would suffice,But sometimes it can also subject to availability of some vacany,I mean if the batch is already sort of crowded,you can't change then