Having customization separate from source code is fairly common with themes for other content management systems I have worked with, not just WordPress.However, it is usually just a change to the way the site looks, not a change to the actual code of how the site operates.The closest analog I can think of in osTicket is the plugin system (same is true of WordPress).If you made all of your modifications into an osTicket plugin, you might have a better chance of being able to retain them across osTicket upgrades. I say 'might' because I've never made an osTicket plugin, and new versions of osTicket have broken people's plugins in the past. On the flip side though, I've been using the LDAP plugin since 1.9.4 and it still works.