Is this the same situation that you were having previously?
Are they still trying to get you to move your days to accommodate a CO employee moving into your current shifts?
Cash office does come under the same umbrella as CSD, however if they move that person to CSD permanently then they will be put on the higher rate, as the request is theirs and not the employees to move.
Again, if you are not contracted to Saturday's, and have no availability stated for that day, then they would have to PROVE it is a " needs of the business" situation. Just to accommodate another person is not a needs of the business, as they should be having that person fitting into the required Saturday shift.
From what I recall from your previous posts on this, the colleague from the CO is unable or unwilling to do certain days, and you are being told you have to move your shifts to accommodate this colleague taking your shifts??
Again I urge you to seek the help and assistance of a rep regarding this.