Multiprocessing systems having changeable CPU configurations generate unique changeable identifications (ID's). These are presented by I/O channels over various I/O connection paths, in association with special path defining commands and function data. Related path state indications are stored peripherally in path map tables and define path group associations for sustaining path-independent I/O operations. When a device is reserved via one path in a path group the reserve affiliation is extended automatically (in the path tables ) to each path in the group, thereby rendering each path accessible in a reserved mode. The path defining commands are used for adding paths to, resigning paths from and disbanding groups. Special sensing commands are used for sensing path reservation and grouping states. When a command for adding or resigning a path is presented to a reserved device via one path in a group the reserve is automatically realigned to the enlarged or reduced group. When a command for disbanding a group is presented to a reserved device the reserve is realigned to apply only to the path on which the command is presented. The foregoing special commands are required to be obeyed by the device even if it currently has a conflicting allegiance to the same system or another system. Consequently, paths can be added to an established path group without requiring potentially premature release of any allegiance.