[Mark McLeod]

Yes, an item can be returned to store condition and count again as COTS.

For instance, I ordered gas shocks that came as a shock, a separate tip, and an activator that screws onto the end.
I put the three pieces together and it was no longer COTS even though it just looks like a gas shock unattached to any new parts, because I could not buy it already assembled.
I unscrew the pieces and it is again as it came in the box and is COTS, because that is how it was bought.

But not machined items like cutting down a shaft or lathing for a clip.
Anything irreversible makes it forever a fabricated item.