Sir, i understand your query as i would like to give some information about csab special round and JOSAA as follows:

The CSAB special round is conducted for fulfilling the vacant seat in some niit or else. So if you are alloted with the college during  JOSAA and you are not willing to take the admission in that one you can cancel it and go for the special round CSAB but remember that in special round CSAB is to fill the remaining vacant seat of colleged and  you are alloted with the seat in round 7 of JOSSA.

Please ask me in comments for further query.

BEST OF LUCK!!