You can download the source for most packages in the Ubuntu Repos. To compile a package from source, you would do something like this:

sudo apt-get build-dep doodad

This will install any dependencies. Now download the source code:

apt-get source doodad

cd doodad*

Edit debian/rules to customize the build process:

$EDITOR debian/rules

Finally, build it as a .deb (for easy uninstalling/dependency resolution):

dpkg-buildpackage -rfakeroot -uc -b

(the arguments will tell the command to fake root, to not sign the package, and to not include the source)

Now you can install the package you just built with this command:

cd ..

sudo dpkg -i doodad-<version>-ubuntu-<crap>.deb

(make sure to install the non -dev version)

Then you can clean up with:

rm -rf doodad*

This was tested on Ubuntu 12.04, with the irssi package. Your results may vary.