Originally Posted by skywardhunter

Generally, yes. Some airlines are more relaxed about allowing this kind of free change if they have space available, I used to do this regularly on JNB-CPT coming in from an international flight where there was an earlier connection to CPT I could make, often switched, no issue, no hassle, done at the check-in counter.

EK are notoriously by the book, however. You might get lucky, but don't expect to. If the later flight is oversold and someone with brains deals with you they might move you for free.