Could the default be altered on a package instance basis, kind of like the default-master?
default templates on a per package basis backed by a master default is possible like so:
[ad_parameter default_template -default [ad_parameter -package_id [apm_package_id_from_key acs-templating] default_template]]
I've used this principle in the authorize-gateway package so that calling packages can rely on the master defaults of the gateway or choose to overide those parameters.
/Bart