Instead of a 1 off solution, I would set it up so you can easily select and run a "Change consultant" process any time without uploading a new BSV.
Something like this might work:
1- Create a form to store two attributes:
a- RegularUser.Consultant_Old
b- RegularUser.Consultant_New
2- Update #1 with the proper Consultant info
3- Run process with this rule:
FIND Client WHERE Client.Consultant=LoggedInRegularUser.Consultant_Old
Client.Consultant=LoggedInRegularUser.Consultant_New
I THINK this should do it.
Of course, before running something like this on a live database, I would first do a backup. I would also be sure to try it on a test system first.