Debian Programming :: Editing Postinst In Existing Binary Packages

I have lately found myself setting up a number of PXE installation servers sufficient that I'm now inspired to automate the process. I've not done this before, but I think I've hit on a method to make it work. I'm using three packages from the archive as a basis: tptpd-hpa, isc-dhcp-server, and nfs-kernel-server. Up to now I've been installing these with APT, then modifying their configs (or creating same as necessary) and then copying my install files (pxelinux.0 and friends, with Debian Wheezy netinst and Xubuntu 14.04 menu options) into /srv/tftp. It strikes me that, rather than letting these packages' postinst scripts do a bunch of stuff that I will subsequently undo, I should modify the scripts in situ to do what I want. I don't feel that I adequately understand how these things work, so I'm asking for advice.
So far I've hit upon two different methods.

I can use apt-get download to fetch the packages, and then dpkg-deb --control to pull out the control files. Then I can edit the postinst scripts as necessary and dpkg-deb --build a new package from the results of dpkg-deb --fsys-tarfile plus the altered postinst scripts. I have gotten as far as extracting the control files from a package, but I'm unsure that the dpkg-deb --build step will work as I expect. Alternately I can do apt-get source [packages], edit the postinst scripts in the source, and then build the packages as usual. I'm more confident that this will work, but I'd rather provide the former method if possible. Is there another method of which I've not thought? Is this the way metapackages are made and configured?