Oy, sorry for the multiple corrections here. APM's actually a little different. The APM callbacks are for specific, one-time events for specific package versions. I'm pretty sure we wouldn't expect to invoke the "after-install" callback for acs-content-repository v5.1.0 multiple times with different arguments. The same can't be said for a hypothetical "on member state change" for user 123456.
It's also worth pointing out that "naming conventions" have worked well for ad_page_contract and acs-templating
(the template::widget::BLAH procs and ad_page_contract_filter_proc_BLAH procs are good examples of what I was thinking of).