I assume you mean you want to override the instance 0x1055 (Sub - Handle Aging Sims). For that, you'll need a new package file with just that BHAV instance. (To do that, extract that instance, create a new package, then add the instance to your package. Click save, then select the instance.)
At this point, you can safely modify-commit-save whatever behavior you want to change. For example, if you want Zombies to be included in the Age Transition routines, you would change where it says something like this (line 8 ):
Zombie - Is Sim a Zombie?(Stack Object); true: B, false: 9
To ignore Zombies here, the simplest way would be to change the true target to 9 (the same as false).