how to rewrite a X- mailheader while routing e-mail

Our problem is that at the moment we use a X-AMC-SpamScore
mailheader to indicate wether an e-mail is SPAM.
Our ISP also has the ability to do spam detection for us,
but they use X-SpamScore as mailheader.

So if we switch over we would like to rewrite the header
name but not the score, so
X-SpamScore: xxxxxx
should become:
X-AMC-SpamScore: xxxxxx

That way we don't have to make changes in our tools
and in the LDAP (where mailfilters are configured).

Is this possible (i suppose through milter), is there
code that i can use / reuse ?

thanks in advance,
Ewald...

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Ewald Beekman, Security Engineer, Academic Medical Center,
dept. ADICT/AD Server en Netwerkbeheer, The Netherlands