Surely, however, depending on the rules applicable to your original airfare, a change fee may apply. I've had airfares on some airlines where there was no change fee, and I've had airfares on some airlines where the change fee was 100% (i.e., if I changed anything about my reservation, I'd basically have to pay whatever the new airfare was in total -- the amount I originally paid would be forfeit.)
You'll have to check the rules on your specific airfare. If the fare has gone down $75 and the change fee is $100, then you're better off doing nothing, eh?