Just put the new one into a group and put a popup menu item to switch between the two (or some other method... perhaps a Function key).

Note that you should be able to just use a single group... enabled, it will not use the normal dns info and display the new info. Disabled, it will just display the normal dns information. I'm not entirely sure if this works or if it will display the normal dns information. Try it out.

Here are two methods:

(This part is the same for both methods)
Code:
#newdns on
on *:dns: {
  [use your dns code here...]
}
#newdns end

Method 1 (menu):
Code:
menu * {
  Toggle New DNS: {
    if ($group(#newdns) == on) { disable #newdns }
    else enable #newdns
  }
}


Method 2 (Function key-- F5):
Code:
alias F5 {
  if ($group(#newdns) == on) { disable #newdns }
  else enable #newdns
}