I can't find anything that describes how to safely customize a module in OTRS.  I want to be able to modify a module and not worry about it getting overridden in a future upgrade.

For example, I've made changes to AgentTicketZoom.pm.  If I ever upgrade OTRS, it's just going to get replaced.  How do I prevent this from happening?

Thanks,
Justin Noel
http://www.calendee.com