hmmm that doesn't sound right. I've not got the tow bar fitted to my F31 but had it on my E91 M Sport and it was hidden behind the rear diffuser. To release it there was a button hidden in the left side of the boot. To put it back you just pressed the button again and then manually push it back.
There was nothing to cut as long as it factory installed. On the F31 I can see the button fitting is in the same location.