If a person has already taken a seat, he can't be dellocated of it although you might be given preference if he needs to upgrade and has a worse rank while you are looking for a new seat, probably.
Anyway, once AIEEE counselling(at least first two rounds) take place, in the Thapar counselling after that you may just scrap through electrical/mechanical. Howevver the value of electrical as a course is much lower than that of civil.