Your preferences are attached to a booking at the time that booking was made/ticketed. If you have a change of heart about your preferences you can change them in your profile but this does not normally affect existing bookings.

You need to contact QANTAS and request the new preferences be entered against each individual booking you currently have. (Strangely enough, this does not always work; I have done this at times, but still ended up with the original preferences etc.)

This goes for special dietary requests as well.