[exim] Was to remove the words Spam: from a subject line?

Due to the use of TrendMicro which is marking messages it thinks might be
spam going out to the Internet with "Spam: " to the beginning of the Subject
line, I am looking at the possibility of having one of our Exim transport
machines strip that that before passing it on.

I know how to add to a subject line, but not quite sure if there is a way to
remove something from a subject line.

Example Header:

Subject: Spam: Test

Where the original Subject line was:

Subject: Test

As of the moment, I can't do anything about the Trend Micro decision.