I think you need to add more specifics. What hardware & software are you running, how heavy a load is on the system (one way to get the load is this bash-level command: top -n1).
Also what are your plans, needs & concerns?
- Are you going to do this overnight or during the work day?
- How many phones per hour?
- Do you need the phones to re-register in 5 minutes or overnight?
- Will the phones unregister & re-register "at the same time" or spread out over the hour(s)?
- Are some users more important than others? If so, what are the needs for each group?
The greater the load, the more stress on the system. Older software (& hardware) responds to this activity worse than newer software (& hardware).
If my job depended on this, I'd either do it off-hours or I'd think about talking to the Avaya developers.
steve