[exim] My first exim configuration

Hi all. My name is Maxi and this is the first time I have to do some work
around a MTA.

I use as a primary email server my Google Apps account, but I need to
achieve something very specifiy which I cannot do with them. Therefore, I
configured Google Apps to route certain specific emails throught my server
instead of theirs. At this point I managed to send an email from a Google
Groups, route it to my VPS (without SMTP auth) and have exim process it and
send it.

Now I need to modify the "From" and "Cc" and I'm lost on how to start. Been
browsing for hours but I'm obviously lacking the basics. Emails sent from
Google Groups come with the following headers:

From: group_name@???
To: group_name@???
Cc: some@??? (the actual legitimate destinatary of the message)

and I need them to be:

From: another@??? (a different domain which I own and manage from
this VPS)
To: some@???
Bcc: group_name@???

So, is this possible to achive? If so, could someone please point me in the
right direction on how to address this?

Sincerely appreciate your help.

Maxi