Morning,
It is quite common for Iberia to change there regular equipment (A320) over the weekends for something else, either to boost capacity or to have the bussen free for maintenance. Nothing strange about that.
As for the engine change...guess they just had one of those bad days there. Given the fact that Madrid has been well below zero the past few weeks, that should not take them by surprise in Linate. But yeah, the 75īs are getting old...should be retired from the Iberia fleet in a couple of years.
Adios