I would think it is yes, just because you can upgrade Magnetic and other OoW player made items after they have been attuned. The only problem with that is, the person who attuned the item, is the only one who do the combine, since the items become No Trade once attuned.
If no one gives a definitive answer in the many hours I'm gone, when I get back, I"ll have my favorite aug upgrader test it out on crappy *flow aug to verify what the status is.
Yther Ore.