It depends on the program but you should be able to send one program, combi if you need to. In general though, you are right. You download an entire Bank and it overwrites everything on Bank A. You can either reload the original Bank A through your synth or save a sysex of Bank A. Then you would upload it to your synth. I'm not sure about x-edit but you need an Editor/Libraian program. This will allow you to save all the banks. Actually, programs such as Cakewalk allows you to save (256?) banks in sysex.