Part of the reason for EO's is that the structural requirements for the mount has changed.
EO's also ensure that other modifcations incorporated in an individual aircraft do not affect the performance of the system such as having antennae installed too close together or inapproprite locations.
Will also address weight and balance changes.
The new beacons require a a much stiffer bracket and specify a maximum amount of deflection of the bracket under a given load .
I suspect this is to ensure the G switch are activated as designed .
IE a flexible bracket would dissapate the shock to some extent.
Most instalations will require additional sheet metal work.
Cheers West Aussie LAME