Hello tzman.
Right now there is no way to limit the package installers architecture, but you can limit the platforms you create an installer for. When you create any package it has an Access Policy associated. This Access Policy contains rules to apply to the package, one of them is the OS availability, there you can select which platforms you want to build installers for, by default we create installers for all platforms. If you have any question please let me know.
Best Regards.
Héctor – SDC Support