May the barrel on an SBR or SBS be replaced with a long barrel with the intent of replacing the short barrel at a later time?

There have been many discussions on this and it appears that as of July 2010 the answer is:
Yes, and you will not be required to again register the firearm before replacing the short barrel. ATF recommends written notification to the NFA Branch when a firearm’s configuration is permanently changed or removed from the purview of the NFA.