Hello!

f you have freezed your B.Tech CST seat in the third round of GGSIPU counselling  it means you have accepted the allotted seat and confirmed that you do not want to participate in further rounds of regular counselling.However yes you can still participate in spot round but to participate in spot round you have to leave your alloted seat that means you will lose your current seat. Then you have to pay fresh fees again for the spot round seat.

Also No upgradation is guaranteed in spot round so if you are 100% sure that you can get a better seat and you are ready to take the risk than you can go for it.