Back to this event: If a PMA turbine blade is heavier than the OEM, would it not be an issue for not only balance, but stress on the supporting disk?
It's not uncommon for turbine blades - even OEM blades (and sometimes compressor blades) that there is a requirement to change them as a complete set - this is often the case when there is a change to the blade design to improve durability and/or performance. It's not just balance, it can be things like blade cooling (if they are not changed as a set the new blades my 'hog' cooling air meaning the old blades are not properly cooled, or visa-versa).