Can PHP changes made to some of the frontend php pages be persistent over upgrades?

[cdslaughter]

I have made changes to two of the frontend php paged (Items.php) that I want to remain persistent after upgrades. I have been told that it might be possible, but I am unsure how to enable this.
Has anyone had any experience with this?
The changes I am referring to are as follows.

https://support.zabbix.com/browse/ZBXNEXT-4987

Carl

[Atsushi]

Each PHP file will be overwritten during the upgrade, so your own changes will be lost during the upgrade. Also, please note that the original source has been changed at the time of version upgrade, and the change method may change.