I'd also favour to take the change out of default-master and leave it package independent. But, why not offer a default-master.adp with the package, that you can copy over the existing default-master if the package is installed.
Or provide a patch for the default-master.adp that will be executed automatically after the installation of the package (I know, probably even more tweaking of the APM, but maybe it is a good option to offer to execute patches while installing a package).
