Being honest, I do not for one minute believe that the issue of tyre deg was fixed after 1000km of testing, after all, they would only have had 2 weeks to do anything about it, and lead time on parts must be quite a long time. Additional mileage on the car is always a good thing however, so there would have been advantages but they would likely not come to the fore until later in the season.
However, who knows if Mercedes used any new parts during the test?