It is possible that the committee are just making the by-law changes in one lump because this is how a strata manager is telling them to do it. Where I live, we changed our ‘rules’ (ACT-speak for ‘by-laws’) gradually. We amended some, we left some unchanged, we deleted some, we added some. We made these changes over several years giving owners time to consider them all. We also had rules we wanted to leave alone at each step because we did not want to have debate about them while trying to make unrelated changes. Registering incremental changes and insisting to our manager that this is how we wanted to do it was not straight-forward. Most, it seems, do just have a single resolution to rescind an old set and adopt a new set. The ‘new set’ can of course include some rules which were identical or similar in the old set. Certainly this is easier if there is little controversy about any of them. There is then one uncomplicated resolution to register the new set in place of the old set.
As for what you can have in your by-laws about keeping animals, I am not up to date on NSW. Perhaps your old by-law is redundant whether you like it or not due to being no longer consistent with the Act? In the ACT an old rule banning pets would be null and void and of no effect. Here the balance is that our Act says a unit owner must apply for permission to the owners corporation to keep an animal but permission must not be unreasonably refused. Perhaps your Act has a similar provision. If so, have no idea if old pet-banning rules were grandfathered.
Our new pet rule gives automatic permission for certain common pet choices subject to some reasonable conditions while setting out that unusual animal choices still need to be applied for and may or may not be approved by the committee. For extreme examples. If you want a goldfish in a bowl, permission is automatically granted by the adoption of the rule; if you want to keep an elephant, you must apply to the committee, which will exercise the function of the OC, and which will probably find reasonable grounds to refuse.