I'd like to offer an experience on the contrary.
I am UK based and had a J class BCN-LIS-GRU flight booked as it was a cheap fare with the intention of positioning to BCN from UK. Originally my flight was booked to depart BCN early in the morning connecting to the daylight LIS-GRU flight arriving in GRU that evening. TP subsequently cancelled my LIS-GRU flight and rebooked me on the overnight LIS-GRU flight the same day meaning I would now depart BCN for LIS at 14:00.
I decided I would actually prefer to leave a day earlier than scheduled to still arrive in Brazil the same day as originally planned. So phoned the call centre.
I had a very short wait to speak to an agent and not only was I offered a change of date I was
also offered a change of departure/arrival airport anywhere within the same zone. I jumped at the chance and immediately changed my itinerary from BCN-LIS-GRU-LIS-BCN to LHR-LIS-GRU-LIS-MAN. The agent was incredibly polite and efficient and within an hour I had my new tickets emailed to me.
Saying that within three days of that phone call I received another email that my LHR-LIS flight had now been cancelled and I had been rebooked on an earlier departure
But as far as the call centre goes, I was impressed.