I believe if you do not have any AC devices installed that qualify for the free 2017 AS, you can select the 2016 version from the drop-down "Versions:" selection box.
ASchoice.jpg
The 2016 version should not require a firmware upgrade.
If you do have recently installed AC devices that qualify for the 2017 AS, you may need to temporarily disconnect them because the 2016 AS may not be offered.