Modifying existing packages

[Jerry Stuckle <jstuckle@attglobal.net>]

Hi, all,

I'm new to this end - and don't know if what I want is possible or not.
But here goes.

I need to modify some of the stock Debian packages for different
options.  For instance, I need to modify
Exim to include MySQL support.  I have several other packages with
similar needs.

What I need is a pointer to instructions on how I can get the the
information for how these packages
were built so I can modify them to meet my needs.  I'd like to change
them as little as necessary to
maintain compatibility with other packages.

I've looked through a lot of documentation and haven't figured out how
to get the original build
information.  But with all the available info out there, I probably
missed it, also.  So if someone can
at least provide a pointer to doc on where I should start, I'd
appreciate it.

TIA.