[Koha] Question about GPLv3 and AGPLv3

I have installed Koha in a local library. Our installation is only available on our local area network, not exposed to the internet. Early on we had a request to be able to print our library cards and spine labels in a format that was not possible by Koha. So I made some minor changes to the label and patron card routines to produce what we needed. I'm perfectly willing to share the code I modified, but I don't think I know how to re-package it as a source tar-ball. If we go to GPLv3 or AGPLv3, would I have to make available the whole source package? I know that a number of libraries have modified the CSS and the front page. Would they have to make the whole source available? -- Bob