This is actually pretty easy to do with the 250.
1. Create a Phantom Ext. And name it something like 'HR Fwd'.
2. Create three Call Routing Announcements (HR Normal, HR Delay, HR Closed) and record your greetings.
3. Point your 'HR line' DID to the Phantom extension.
4. Use the Remote Programming feature (359) to forward the Phantom to one of the three CRAs - 359 (phantom ext) (phantom ext’s password) 355 'fwd all calls' (CRA Ext).
5. Set another DID as DISA and set a password.
Now the customer can call the DISA DID and use the digit sequence above to change the destination of the phantom ext.
If your customer has a public IP pointed at the system, you can create a DEE user for the Phantom ext. and they can change the forwarding using the web interface.
Also, you can use station speed dial to enter the digit sequence for each mode and program SD buttons to make it easy for the attendant to change it from the office.