I have a trip planned to SCL for later this year. I only intend to fly with cabin luggage - which might narrowly exceed both the weight and size limit.

How likely is it that Iberia wouldn't care about it?

The reason for asking is that I intend to skip the last leg of my trip (MAD-FRA). If for some reason they decide that my luggage is too big/heavy, I would have to check it in and go all the way to FRA - unless there is some magical way of convincing the staff to only check it in to MAD (which is probably unlikely, as the connection is supposed to be <2h).

Any advice?