The communal HWS I assume is one system supplying all lots (as opposed to individual HW tanks mounted on roof) and so it would be Strata responsibility.
You could fit tempering devices within your lot at your cost but to do it to the HWS on the roof would be a Strata responsibility and as the technical note only applies to new systems their would be no requirement for the Strata to do anything.
You could submit a motion to the OC to have a tempering valve fitted centrally by the OC but this would require a Special Resolution as it is considered an improvement (75% in favor).
As this would improve the system for all users they might go for it.