Hi
This is possible so it must be done manually
1º Run command omnidownload -libraryLibraryName-fileLibConfig...save a copy of Libconfig file
2º Edit libconfig file and rename path for files that you want move for example X:\tape_001 to z:\tape001
3º Move fd files from one disk to other disk cut\paste
4º Run comamnd omniupload -modify_library Library -file LibConfig for modify library configuration.
About file depot selection is controled by MMD process and can not be controlled manually. The theory says that file depot with more free space will be used.