[gentoo-user] managing local IP's

I have two networks connected over VPN

1st Network has 3-box (only one active)
2nd Remote Network has 4-boxes (only two active at any given time)

All boxes are configure to run: Hylafax, Asterisk (but only one at a
time act as a server).

Various external devises like Sipur, Audiocodes has to be configure (IP
change) to register to Asterisk server; if I switch a box that acts as a
server, I need to login to each device and change the IP.

Hylafax is relatively simple to switch, but "yajhfc" that view the faxes
has to have an IP changed.
Audiocodes - is a nightmare to change IP.
Local Asterisk registers with Remote Network over VPN so IP's need to
change as well.

Is there an easier way to mange it?

-- 
Thelma