If you are lucky you can add PROCESS to the Template config in Bugzilla/Template.pm and it will run when ever you put in there whenever it processes a template.

    PROCESS  => 'tricksy',
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and make templates/en/default/tricksy

<!-- [% template.title %] -->
[% PROCESS $template %]
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If you are not lucky, then you will need to sub-class Template::Service and set $Template::Config::SERVICE = $mysubclass; before the Template is instantiated.