Finding out relevant information in the new CASRs about a single topic is like completing a 1000 piece jigsaw with the pieces scattered around the backyard. Anyway these are some relevant pieces of the Overweight Landing jigsaw that I have found. Note that my list is most likely not exhaustive and that I'm looking at it from an Airbus pilot perspective.
CASR98 regulations that govern landings include:
91.095 & 121.055. Require the PIC (91.095) and the operator (121.055) to comply with the AFM.
91.800 & 121.420. Require the PIC (91.800 & 121.420) and the operator (121.420) to comply with the relevant MOS.
Part 91 MOS 25.02. State that the PIC must use a specified method to calculate landing performance (Airbus = Flysmart).
Part 121 MOS 9.13. Specify the inflight landing distance requirements (including a 15% factor).
The combined effect of those regulations is that since:
the Airbus AFM (ie the FCOM) includes an Overweight Landing procedure, and
we can calculate an inflight landing distance at weights in excess of the max landing weight, no special circumstances (ie an emergency) are required to land overweight.