If the calls all pointed to VE 600, then use MB 24-09 to call fwd all 600 to the outside number.
Or, set up a night mode with a night button. Set MB 22-02, mode 2 to DIL. 22-07 DIL to a virtual, then CFA to the outside number. Place a night button on a phone, assigned as option 0, (follow setting in 12-08). Toggle the button for day/night mode.
A more complex way it to divide your DID translation tables and use those to send calls to the outside number.