This happens very rarely, and is usually of the same family. You replace an Airbus 320 with another airbus, not a boeing. Simply because those airlines don't have both on them in their portfolio.

Now if its specifically to avoid a certain type of Boeing 737 max when the airline already flies boeing, yeah thay might happen indeed.

The only cases of switching families is long haul, like Emirates replaced an Airbus a380 with a 777 once on a trip I took. Still caused massive issues because the boeing is smaller, so they don't like doing this.