I don't know about other concert pianists or how they operate these days but Horowitz took both his piano and tech with him. You can find Youtube videos of one such excursion where they interview his Tech stage side. They moved the piano from his livingroom in NY and transported it to Europe, the tech did a pre install tuning then they hoisted the piano on stage where he tuned it again. I imagine in most cases if it's a two day show it gets tuned before each show for anyone pro level. Horowitz only played his own Steinway tuned by his own tech, voiced to his own liking.
Locally we had ourselves a star pianists named Ken Manzer who did some classical and Chopinesque pop make overs in his own club. I can remember him during a break touching up the strings himself. That's when I got the idea, if he can do that so can I between tunings in my own livingroom ( forget the entertaining part, he was in another league) and so it began that I learned to tune my piano, FWIW.