In newer versions of openacs, there is an added feature which implements "weak inheritance of a package", which at least allows templates in one package (the "inherited" package) to be used from another (the "inheriting" package).
One specific use has been to inherit from subsite, and in fact the APM has been altered to accomodate the specific case of a package that somehow implements subsite semantics, either of its own accord, or thru inheriting from another which (somehow) implements subsite semantics.
For an example of this, see: layout-manager and layout-managed-subsite.
If you play with this, you might find there is a whole new layer or set of layers that make it so that alterations don't need to be in core.
-Jim
