If the BAEC change/cancellation structure does not work for you, then perhaps you should look at alternative programs. AAdvantage has much higher cancellation fees for example.
But no change fees, so would be easy in this case
Different schemes have different rules; should expect the rules of whatever scheme choosing to use to apply. If BA has a fee for the change, then c'est la vie; no reason to rant about it being a ripoff and the good old "nick and diming" phrase when a company charges its fees