I use my Core bar on my 7m Best kite from time to time because it has a shorter bar,flys fine, the important thing is that the lines are all the same lenght,eg the power lines and the steering lines are the same,

not sure how it affects the safety system on the North kites

try activiating the safety system by releasing the kite in LIGHT winds and see what happens,if it flags out and depowers,I think it would be fine