[Exim] Perl Function to remove Headers

I am trying to do the "central_filtering" below. But instead of using a filter file,
I'd like to call a perl function. This perl function would do some mysql lookups/
updates, and alter the headers.

Main question: Is it possible to have a perl function alter headers in the message.
If so, how?

Thanks,
-Allan
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From the Docs:

39.8. Per-address filtering

In contrast to the system filter, which is run just once per message for each delivery attempt, it is also possible to set up a system-wide filtering operation that runs
once for each recipient address. In this case, variables such as $local_part and $domain can be used, and indeed, the choice of filter file could be made
dependent on them. This is an example of a router which implements such a filter:

  central_filter:
    driver = redirect
    domains = +local_domains
    file = /central/filters/$local_part
    no_verify
    allow_filter
    allow_freeze
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<- Allan Rafuse ->
Systems Administrator
Equat.com Technologies
email: arafuse@???
web: http://www.equat.com