Customized mail wrapper

We are working with zammad 4 and have customized the ‘application_wrapper.html.erb’ to add a company wide html formatted footer to meet the corporate identity. Everything works as expected. But after upgrades the file is overwritten.
I’d like to have a ‘application_wrapper.html.erb-custom’ or similar which is used if exists and not being overwritten while updating some packages.
Else I need to edit the file after every upgrade.

A erb-custom file would fit my needs, an option to edit the template in html inside zammad would be more comfortable.

Or do we have any other options?