Hmm... perhaps I misinterpreted (sort of) the documentation of udev at
Writing udev rules.
There it says "In general, you want your own rules to be parsed before the defaults, so I suggest you create a file at /etc/udev/rules.d/10-local.rules and write all your rules into this file.", which I interpreted as, the sooner the rules file is read the higher priority for the rule.
Simply renaming my rules file to "99-zzz-local.rules" solves the problem since it will then be last to be parsed and it's rules will be the ones in effect.