Hello Aspirant,

See as you have not mentioned the name of state so it is little bit difficult for us to guide you with an accurate information because different state have different rules and regulations for Mop-up round of NEET UG counselling but commonly, with most of the state counselling authorities, if you don't accept the allotted seat then you would not be allowed to sit for mop-up round and if you accept the seat then you can apply for upgradation of seat.

So I would recommend you to join the seat and then you can apply for upgradation of seat in mop-up round and if you get an upgraded seat then the seat allotted to you in earlier round would be automatically cancelled and allotted to another candidate but in case if you do not get an upgraded seat then you can retain back the earlier allotted seat.

But before going through any of the above process first of all check out the norms of the respective state counselling authority.

I hope this information helps you.

Good Luck!!