I assume it happens regularly. I had a couple of flights myself on other plans than initially advertised. I always assumed that the airline canceled/delayed other flights because of it (taking plane a and crew a from flight a to do flight b with plane a).

Before the 737 Max got grounded (after the 2nd crash), I remember reports that some airlines allowed passengers to rebook their flights for free (to end up on a different plane). I doubt they will continue doing it once the 737 Max is allowed to fly again. Eg, Southwest is too dependent on it.