I want to SBR my FN 16s and want to install a 10.0 Barrel after I get my Stamp in the mail from the ATF. I am filling out the ATF, (Application to make and Register a Firearm), I think this the Forum 1 ? What Question (j) mean? Is this firearm being reactivated? I answered NO. Is this correct?
From the 1k definition:
k. Reactivation. The restoration of a registered unserviceable NFA firearm to a functional condition. This action incurs the making tax liability.
Unless you’ve had it previously registered and it has become unserviceable the NO is the answer.
It’s amazing what people could learn from actually reading the forms. 
Thank You, that is what I thought question was asking and answered, No.