Thank you for your reply.
Could you please explain exactly which files should have changed?
I see that the SERVER_IP_REPLACE variable is instantiated in ur_driver.cpp, external_control.urscript and ros_control.urscript. But the external_control.urscript is part of the externalcontrol-1.0.5.urcap that is installed on the real UR. So shall I change the installation urcap? or will the ur_driver.cpp be enough?