I just investigated the "skip cooldown" bug, because, well, that would be bad. But as far as I can tell, you cannot actually use it to rebuild faster.
What you're seeing is solely a bug with the animation client-side. The time between rebuild hits is independently checked on the server, and that check is not affected by this. In fact, if you watch closely while doing this and are actually doing it fast enough to beat the animation, you'll see that the rebuild meter doesn't actually fill in response to the extra hit.
I'm guessing this was on a Squid? It really does only take about 3 seconds (4 hits) to rebuild the Squid's armor with the Shifting Spanner.