A small temp change may stress your fish, but shouldn't kill any. A 30% water change, even with adding water 2 degrees won't change your water temp that much. Most fish, cichlids included, have a normal range of temps in which they are comfortable, but getting out of the range, unless it's an extreme variation, won't hurt them short term. And, cichlids in general are pretty hardy fish, especially New World cichlids. I'm sure your convict will be fine.
150g long S Amer cichlid; 90g C Amer cichlid; 90g Malawi cichlid; 40g Tanganyika cichlid; 29g "Shellie" cichlid; 29g Pea Puffer. 6,500g koi/native catfish pond; several smaller ponds