I'm a huge fan of "the Debian way" (https://wiki.debian.org/DontBreakDebian)
Part of that is imho that you should have the option to not modify the default config files of any package, and rely instead on a default . This has the precious advantage that you may let the original package maintainer keep the config file as he desires and keep meaningful changes for the future; in example new default values for a major release 3.4->4.0
To make practical examples: There are three common Debian packages which do exactly this: MySQL or MariaDB, Dovecot (the popular IMAP Server) and the Zabbix Agent from repo.zabbix.com !
And to compare those three examples with the zabbix_proxy.conf from Zabbix 4.0 alpha6:
As you see, there is no way to write your own Zabbix Proxy conf files, without editing the original file. This annoys me, cause Debian will ask me if I want to keep my modified zabbix_proxy.conf or overwrite it with the maintainer's version everytime there are significant changes.
So please add a default include like:
to your repo.zabbix.com deb files
In comparison to the Zabbix Agent deb files, the Zabbix Proxy deb package lacks a default include for additional conf files.