Just a data point. Today I cancelled a booking with NC-6 TP from Marriott's website. I totally forgot that this reservation has TP attached. After cancellation, it says 165,000 points will be credited to my account. I got scared since I do not want the points, but the TP de-attached. But when I check my account, I see the NC TP was returned to my account. It says "Partial Package -7 nights Cat 6". And it has value of 165,000 behind it.
I figure if the TP has been converted to NC, then it is safe to cancellation from website. But it won't work if the OC TP was attached.