Amazon Man,
The ex-CFE crew did not get a seniority number based on their date of joining at CFE. They went to the bottom of the BA seniority list BUT have date of joining at CFE seniority for employment protection and staff travel as was their right under TUPE legislation.
If the BACC negotiate a scope clause with the company you will not have any right to reject or accept it, it will not be offered to BACX in any way. This is the opportunity that you are turning down, to be involved and have some influence on the process. If the scope deal is sorted out BACX will have to operate outside the process but will be limited by the agreement to the size of a/c that you can fly. You may not like this, I wouldn't, your only option is to get the BACX CC involved again, it is not too late, and get your voices heard at the highest level.
I wouldn't like to be excluded from a process that could conceivably tie the two companies much closer together. I hope that whatever result occurs you are all happy with it. Good luck with the negotiations and please don't cut off your noses to spite your face.